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EAGE-HAGI 1st Asia Pacific Meeting on Near Surface Geoscience and Engineering
- Conference date: April 9-13, 2018
- Location: Yogyakarta, Indonesia
- Published: 09 April 2018
1 - 100 of 115 results
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Case Studies: Identification of Subsidence Problem Using Electrical Resistivity Imaging
Authors N. Yunus, M.H. Arifin and K.I. Abdul RahimSummaryThe settlement problem can cause a major damage to the building foundation thus could probably causing harm to the surrounding area. Therefore, three locations has been chosen to discuss this matter which located at Batu Pahat, Johor, Shah Alam, Selangor and Sungai Siput, Perak. Electrical Resistivity Imaging (ERI) method has been chosen to measure the resistivity of subsurface materials and identify the causing factor of subsidence at these locations. The instrument used is ABEM Terrameter SAS 4000 System. Resistivity profiles showing the subsurface condition of the study area which indicated various factors that causing the subsidence at these areas. Remediation process must considered several factors including suitability of proposed method including the causing factors, lithology and severity of the damage.
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Travel-Time Tomography Imaging around Sinabung Volcano during 2010–2017 Eruption Period
Authors A.T. Sasmi and W. SuryantoSummarySinabung Volcano, which never shown any certain volcanic activities since its last eruption in 16th century, suddenly errupted at August 29, 2010. The disaster has not just stopped. Sinabung eruption repeatedly occurred at 2013, 2014, 2016, and 2017, with unstable change of eruption statuses. This research is aimed to identify relationship between Sinabung Volcano recent erruption activities, with distribution of P-wave anomaly around Sinabung Volcano.
Seismic velocity values are derivative form of travel time value. Some factors which influence a seismic velocity condition are lithology type, rock density distribution, rock porosity, rock depth and pressure condition, also fluids saturation in study area. This research was implemented using earthquake travel time data of January 2010-May 2017 period, from Indonesian agency of Meteorology, Climatology and Geophysics (BMKG) earthquake catalog. Data processing was done by Simulps14 program to create distribution map of Vp anomaly from the targeted area.
The result showed that vertical variety of P-wave velocity beneath Sinabung Volcano indicates relation with partial melting zone and fracture which were formed at the end of 2013. This features led Sinabung into big eruption at January 2014.
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The Application of Magnetic Resonance for Formation Pressure Tester and Stimulation Optimization in Produced Carbonate Reservoir
Authors Cahyo Nugroho, Viet Le, Al-Turkey Shaikha and Mohammed Ali Al-IbrahimSummaryA producer well with tight carbonate reservoir was planned for stimulation with objective of production improvement. The strategy for the stimulation was hydraulic fracturing in a fishbone completion. Magnetic resonance and formation pressure tester were used to evaluate fluid content, rock quality and formation pressure of the reservoir. The magnetic resonance had helped to identify the formation pressure tester points and resulted all good test in tight carbonate. The magnetic resonance had delivered remaining oil saturation and rock quality in regards to porosity and permeability. The oil saturation and rock quality were integrated to choose the sidetracking intervals of fishbone completion. The fishbone completion was to be stimulated with hydraulic fracturing to connect the good oil saturation and rock quality intervals, and to enhance permeability of fair rock quality. This application is first use of magnetic resonance in a revisited producer well of tight carbonate reservoir.
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Identification of Heat Source and Alteration Zone of Parangwedang Geothermal System using Magnetic Method
More LessSummaryResearch using magnetic method has been done on geothermal area located in Parangtritis, Yogyakarta. This geothermal system is often called Parangwedang geothermal system. This research aims to map alteration zones and predict the existence of heat source in Parangwedang geothermal system. The research was conducted by acquiring magnetic method data on 2x1 km2 area around the manifestation of parangwedang hot water with measuring point in the form of uniform grid with the number of 174 points of measurement and spacing between the points 100 m. The result of the magnetic method is a total magnetic field anomaly map that will be analyzed qualitatively to determine the extent of the alteration zone and the predicted presence of heat source. The alteration zone is mapped to a low magnetic anomaly located in the southwest of the research area. The existence of heat source is suspected to be in a high magnetic anomaly located just below the manifestation of hot water parangwedang.
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Evaluating problematic landslide-risked site using hydrogeophysics, isotope and conventional hydrological techniques
SummarySlope failures, landslide and settlement of foundation (subsidence) typically do not occur spontaneously. In this context, the task of predicting the exact failure is difficult, as the point of ultimate failure is dependent on a number of factors ranging from geologic structures of the area to land use change. The first stage in any assessment of a landslide-risked area is the establishment of a reliable conceptual model of the subsurface conditions. Here we present initially results from a study conducted at Bukit Tinggi National Secondary School, Pahang, Malaysia prior to the likely occurrence of landslide activities. Our focus is to evaluate problematic subsurface of a natural landslide-risked using integrated geophysical, isotopic hydrology and conventional hydrological techniques. In this preliminary stage of the study, field screening began with minimally intrusive techniques: electrical resistivity tomography and seismic refraction surveys. The results of geophysical techniques are supported by the isotopic signature which may give a direct insight into the origin and distribution process within the hydrological system. It can be concluded that these techniques complement the conventional hydrological and hydrogeological methods employed in problematic site assessment and their use should be encouraged.
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Geotourism Development Planning in Paleobotany Park Merangin
Authors A. F. Bobbybuana, S. Dwiputri, M. I. Pribadi, R. A. Puteri, I. Azizah, A. M. Fath, B. Ansori, A. Sidik and D. SaputraSummaryGeopark Merangin Jambi located in the Jambi Province administratively. The total area of Geopark Merangin Jambi is 20.360 km2. Currently, Geopark Merangin Jambi is in the process of being certified as Global Geopark by GGN-UNESCO. The Paleobotany Park Merangin with whole area of 1.551 km2 is present as a core region and is situated in the southern part of Merangin Regency, typically along and in flood plains of the Merangin and Mengkarang Rivers. The main obstacles found in Paleobotany Park Merangin based on Author’s observation results are poor accessibility to geosite locations and inadequate management. This constraint is due to the lack of attention from the government and the public awareness to preserve geosites even though Geopark Merangin Jambi is currently in the process of being certified as Global Geopark. Therefore it is necessary to plan the development of geotourism in Geopark Merangin Jambi, especially in Paleobotany Park Merangin as a core region of Geopark Merangin so that constraints can be overcome. The aim of this paper is to introduce as well as publication media to increase local income and in addition it can be used by the Government to develop the Paleobotany Park Merangin in the future.
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Audiomagnetotelluric Survey to Characterize the Geological Features of Merren Valley Site, Papua, Indonesia
Authors S. Arjuna, A. Pringgoprawiro and A. SyukriSummaryA drilling plan is quite important to minimize errors during drilling. Information on subsurface geological aspects will helpful in providing supporting information for drilling plan. An audiomagnetotelluric (AMT) survey has been successfully characterized the Merren valley site which is located East of Grasberg mine area, Papua, Indonesia. The AMT survey is aiming to characterize the lithological features and delineate the EESS west fault at the depth as part of wells monitoring drilling program. A total of 57 stations were collected by using Zonge equipment system with dipole 50 m, 25 m spacing between stations, and L shaped configuration. The Zonge software used to produces the 2D electrical resistivity profiles. According to the AMT survey results and comparing with known geological condition of study area shows the near surface layer interpreted as glacial till formation that characterized by a moderately resistivity response about hundreds ohm-m. Meanwhile, the deeper layer that has resistivity response about thousands ohm-m indicated as limestone rock. The EESS west fault zone (lower resistivity) indicated more steeply than fault inferred by conceptual model. The resistivity inversion model appears agree with the geological condition of Merren valley site that can be used for making decision in drilling plan program.
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Damage Zone Map Due to Earthquake on May, 27th 2006 in the Area of the Opak River, Yogyakarta Based on MMI Scale
Authors P. Nurhayati, A.S. Banuzaki, B.S. Simorangkir, I. Ilmawan and D.P.E. PutraSummaryJava island has been known to be frequently affected by earthquake. On the other side, the management of earthquake disaster mitigation is still lack of disasters anticipation and mitigation plan. It can be proven by the absence of detail damage-zonation maps of earthquake. The damage-zonation maps of earthquake are needed to assess the impact of future earthquake. Based on the 5.9 richter scale Yogyakarta earthquake on May 27, 2006, the worst affected region was around the Opak River. Therefore, the damage zonation map of earthquake in Opak River is absolutely needed to mitigate the future earthquake cases. The investigation was conducted by interviewing the earthquake witnesses scaterred in 82 locations along Opak River. The results of interview were classified based on MMI (modified mercalli intensity). By apply spatial analysis in GIS, the MMI data were interpolation and extrapolation to damage-zonation map of MMI. Reveal the result the biggest MMI classes was obtained along the Opak River and controlled by fault continuity, earthquake magnitude, distance from epicentrum, litology thickness and litology type.
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Two-dimensional Magnetotelluric Modeling Based on Bi-tree Mesh
Authors M. Li, Z.Y. Zhang, M. Xin and S.P. XieSummaryIn order to improve FEM forward modeling efficiency and precision of the 2D magnetotelluric problem, this paper focuses on calculating the response of a two dimensional MT model considering the conductivity and permeability variations simultaneously. These secondary fields method used to solve the secondary variations problems parallel to strike like Wannamaker. A model discrete method based on the bi-tree structure was developed and applied.
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Geothermal Control System with Estimated Distribution of Resistivity Value Using AMT Method in Ungaran Area
Authors A. Gilang, A.T. Yuliwardana and A.I. AssidhiqieSummaryGeothermal prospect area of Mount Ungaran is located approximately 30 km southwest of the capital of Central Java, Semarang. The area is physiographically located in the North Serayu Mountains formed by the lifting of the Miocene. This mountain was active between the late Pliocene and the Late Pleistocene. In the area, there is a geothermal prospect located on the southern slope of Mount Ungaran, namely in Gedongsongo area.
Several geothermal manifestations around Mount Ungaran include: fumarole in Gedongsongo area, hot springs in Banaran, Diwak, Kaliulo and Nglimut areas, and altered rocks are found in Gedongsongo and Kendalisodo. From existing research, a geothermal prospect in this area is dominated by water, which is structurally controlled by Ungaran caldera structure. From interpretation AMT, the heat source is thought to be a diorite intrusion with range value resistivity are 2.8–4.0 ohm.m. Cracked volcanic rocks of Lower and Tertiary Quarterly are thought to function as reservoir rocks with range value resistivity are 1.5–1.4 ohm.m. The impermeable upper quartile volcanic rocks are thought to function as cap rocks with range value resistivity are 2.8–4.0 ohm.m. Based on geothermometry on fumarole found in Gedongsongo area, reservoir temperature is estimated to reach 230°C.
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Geology and Geophysisc to Discover Cu-Zn Mineralization in Purwohardjo Area, Wonogiri Regency, Central Java
Authors V. P. Harefa, R. A. Hidayah, B. B. Prabowo, D. Aminulloh, R. A. M. Yudha and B. D. DiliantoSummaryThe research is located in Central Java Province, Wonogiri Regency, Karangtengah-Purwohardjo Area. The lithology unit in the research area consists of volcanic breccia units, which are intruded sequentially by the pyroxene andesite, and the dacite. The geological structure of the shear and fracture faults participates in controlling the mineralization in the research area. Based on interconnected relationships in the field, the dacite is interpreted as a mineralization-bearing intrusion. Hydrothermal alteration includes argillic and propylitic alteration. The argillic alteration zones are characterized by the presence of sericite minerals, chlorite and clay minerals, which are generally intensively formed on pyroxene andesite and dacite. The propylitic alteration zones are characterized by the presence of chlorite, epidote and calcite minerals, which are commonly found in volcanic and partly andesitic breccias. Hydothermal alteration is strongly associated with ore mineralization. The copper ore sulfide minerals are chalcopyrite, bornite with a bit of kalkosit and kovelit.
In Induced Polarization profiles the Trend value of high chargeability appears to be related to the presence of metal sulphide minerals in andesite and dacite rocks. Based on the characteristics of alteration and mineralization and from Geophysiscs interpretation, the research area is included in High Sulfidation Epithermal related to Porphiry type.
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Application of the bilateral filter to improve derivative based lineaments enhancement approaches
Authors J Wang and X. H. MengSummaryIn the work discussed in this paper, we have applied the bilateral filter to improve the derivative based lineaments enhancement method of gravity and magnetic data. The method was tested using the gravity responses of a combined density model. A comprehensive comparisons indicated that the bilateral filter can effectively smooth the original field data without disturbing the sharpness edges. Filtered data obtained from the bilateral filter can be further used for edge detection stably without losing of useful boundary information.
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Lithology and Petrophysic Variations of Carbonate Reservoir Using Rock Typing: Analogue Study in Ponjong, Yogyakarta
Authors I. Ramadhan, A. R. Perdana, P. Herianto and R. HidayatSummaryResearch area shows 3 distinct rock types, RT 1, RT 2, and RT 3 (lacks of data). RT 1 has the highest permeability, compared to RT 2, and RT 3 (lowest). The permeability is very dependent on pores, which has strong relations to diagenetic environment.
Diagenetic processes have implications on pores and cement forming. Cement formed by diagenetic process are bladed isopachous (calcite), formed in fresh water phreatic environment and fibrous isopachous (aragonite), formed in marine phreatic environment. Pore formed by dissolution shows vadose zone
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Geology and Hydrothermal Alteration of Cibeber Prospect, Lebak, Banten: a preliminary study of Au-Ag-base metal sulfide deposit and implication to exploration
Authors C. D. P. Dana, A. Idrus, S. D. Masti, F. Yuniardi and I. A. MeakSummaryThe research area is located in Neglasari, Cibeber, Lebak, Banten. As we know that western Java has a big potential in mineral deposits especially epithermal deposits and one of them was found in this studied area. This study aims to understand the geological and hydrothermal alteration as well as the mineralization characteristic in studied area. Surface geological mapping is used to know the geological condition including lithologies and structural geology also hydrothermal alteration distribution. Five representative ore vein samples were analyzed using FA-AAS method to determine the grade of precious and base metal contents. The lithologies found in this area can be divided into 3 unit stratigraphically that is sandstone unit, tuff breccia unit and andesitic lava unit while the structural geology are strike slip fault, normal fault and some joints. There are 4 alteration zone that is silification zone, clay-silica zone, clay zone and chlorite-epidote zone. The mineralization mostly found as hydrothermal veins which can be divided into two type that is precious metal bearing vein or usually called as low sulfidation type and base metal bearing vein or usually called as intermediate sulfidation.
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CSAMT investigation for geological structures in a HLRW preselected site
More LessSummaryThis paper discusses the use of Controlled Source Audio-frequency Magnetotelluric method (CSAMT) in geological structure exploration at an area preselected for high level radioactive waste (HLRW) in northwest China. The survey objective is to evaluate the rock mass quality and find the weak geological structures which will cause damage to the safety and stability of underground repository. We conducted a dense CSAMT survey, combined with borehole information to delineate the local weak geological structures. The study was conducted in NW China in 2014. The comparison between the interpreted results and geologic information shows that both are in agreement. The preliminary results offer detailed information about the electrical structures of Nuorigong rock mass from the surface to 1400 m deep, so the interrelationship between the target rock mass and its surroundings were analyzed to show their shapes. In conclusion, CSAMT results are helpful in exploring the subsurface for geological structures and competent rock mass. It can also provide the reliable geophysical evidence and scientific reference for complete and consistent evaluation of the deep geological structures, and aid in comprehensive assessment of preselected sites for HLRW disposal, such as further study in the design and construction of an underground man-made repository.
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Site investigation using resistivity survey to investigate possible slime deposit in ex- tin mining area
Authors H. Hussin, M.H. Ariffin and T.A. JamaluddinSummaryResistivity is a well-known method to detect rock resistance value in the subsurface. Its ability to penetrate deep into rock mass have been utilized in various field. In this study, resistivity tomography survey was conducted to identify the present of slime layer in ex-tin mining area which conducted at Kampar, Perak, Malaysia. Slime was a residual material mostly comprise sandy and clayey material. Slime was consider as weak material and can cause problems especially ground settlement. A total of five resistivity survey lines was carried out to cover entire proposed area ( Figure 1 ). Geologically, the study area is underlain by sedimentary and metamorphic rocks which is part of Kinta Formation. Resistivity interpretation shown four different anomalies which are soft layer, compact layer (soil), slime and rock boulder. The present of slime material is deposited 25m below surface.
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Geomagnetic Investigation to Delineate Heat Source of Geothermal Potential in Jambi Sub-Basin
Authors A. F. Bobbybuana, F. Randitama and V. AfrionalSummaryPandan Sejahtera Village, Geragai, East Tanjung Jabung, Jambi, is an object study area to make observations, because the discovery of geothermal manifestations in the form of hot springs with a temperature of about 60 degrees Celcius. The study area is located in back-arc basin which is far away from subduction zone and active volcanoes. In geothermal exploration, Geomagnetic Method used to identify the type of rock that is the source of heat. Interpretation of geomagnetic data is done by using Reduce to Pole and Upward Continuation as filters. In order to calculate those filters, Fast Fourier Transform (FFT) was applied to the geomagnetic data by using Oasis Montaj software. Based on the Upward Continuation filter results the Author interpret that distribution of shallow and deep anomalous zone are respectively associated with residual and regional anomaly magnetic. Deep anomaly in the East - Northeast direction is interpreted to be associated with a heat source because it has a low magnetic anomaly value owned by demagnetized rocks due to high temperatures.
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Determination of Peak Ground Velocity Observation as Geohazards Parameter in North Sulawesi
Authors R. Priadi, D.A. Pratama and R.B. KurniawanSummaryNorth Sulawesi’s activities are mostly done by triple junction between Eurasian, Philippine and Pacific plates causing seismic activity in the north Sulawesi region. In addition to PGA data there is also one parameter that can be used to characterize the ground response during a earthquake that is PGV (peak ground velocity). PGV is the most frequent value in an area within a given time period due to an earthquake. The result of PGV observation value is obtained if the largest PGV value is 0.25667215 cm/s at the earthquake event of Northern Molucca Sea M 4.8 dated 19 November 2016. Then for the smallest PGV value of 0.000187953 cm/s at event Molusca sea M 4.8 dated 5 May 2016 which recorded maximum at north-south component at TMSI station. The average PGV observation value in North Sulawesi is 0.056756952 cm/s. Areas with large observational PGV values are Bitung, Bolaang Uki, and Kotamobagu districts. PGV values are only good for accurately representing intensity and state of the station for earthquake magnitude below M 6.0. For earthquakes with magnitude M 6.0 or greater it is recommended to keep using PGA to represent ground shaking when an earthquake happend.
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2-D time-domain waveform inversion using Gauss-Newton methodology in elastic media, case study: complex marmousi2 model
Authors B.I. Hardi and T.A. SannySummaryFull-Waveform Inversion (FWI) can be defined as an iterative fitting data procedure for obtaining physical properties of the Earth based on the full wave-field data simulation. Hence, FWI is widely known as a comprehensive way to solve the complex structure below the earth surface, it performed a high-resolution image, and very powerful when it combined with the good prior model.
In this research, we especially focusing on how we worked with the 2-D Full-Waveform Inversion (FWI) using Gauss-Newton approach in elastic media. The steps included the forward modeling problem based on the finite-difference and staggered grid scheme that bounded by free-surface boundary condition (on the top of model) and Perfectly Matched Layer (PML) for the rest, also, we applied the Gauss-Newton inversion that exploit the approximate-Hessian into this methodology. For the result, we tested the inversion modeling in simple layer cake model and complex marmousi2 model, both of those models are located in the shallow area.
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Comparison Analysis Of Subsurfaces Survey Between Geophysics Method (Geoelectric/Ert) And Geotechnical Method (Standard Penetration Test (Spt) At Kaima Overpass Manado-Bitung Toll Road
Authors Abdurrahman Wafi, Panganggit Sasmito, Mohammad Arief Rizki and Arief RahmanSummaryManado-Bitung Toll Road is one of priority projects announced by Indonesia President, Joko Widodo, to speed up economic growth in North Sulawesi Province. Kaima Overpass is one of many overpass which will be built to provide crossing between Manado Bitung toll road and local roads around it. Geo-electric method or known as Electrical Resistivity Tomography is used to get subsurface data and groundwater, while geotechnical method is used to get data about mechanical properties of subsurface material. The purpose of this research is to know the structure subsurface, estimated volume of hard rocks and soft rocks at Kaima overpass location. Kaima overpass location is dominated by medium rocks and hard rocks from Geo-electric data with value greater than 500 Ohmmeter and Standard Penetration Test N-SPT value greater than 15. The subsurface material structure consists of Andesite and Gravel Alluvium, which come from sediment / lava sediment from Mount Klabat.
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Determination of Slip Surface area using Geoelectric, MASW, and Soil Mechanics Data in Cimuncang Village, West Java
Authors R.C. Wibowo, B.S. Mulyatno, M. Romosi and A. ZaenudinSummaryThe research of soil movement has been conducted using resistivity method, MASW, and soil mechanical data in Cimuncang, Malausma, Majalengka. The research has done in order to know resistivity distribution value and shear wave velocity VS30, to determine and analyzing rock layers pattern, slip area depth through 2D and 3D modelling result, and analyzing slope Safety Factor (SF) based on soil mechanical laboratory testing. The estimation of resistivity value is done by applying resistivity modelling, the value is vary from 6–200 Ωm which the depth of slip area is 5–7 m. The estimation of shear wave velocity value is done by applying MASW modelling, the value is vary from 40–500 m/s which depth of slip area is about 5 m. The layer that used as slip area based on resistivity modelling is contact between clay (<25 Ωm) and tuff (25–75 Ωm), and based on MASW modelling that considered as slip area is between soft soil layer (VS <183 m/s) and stiff soil layer (VS 183–366 m/s). Based on Geoslope modelling gained slope Safety Factor (SF) is valued 1,26 in southeast that means the slope is relatively stable and in northwest is valued 0,98 that means the slope is unstable area.
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Preliminary 1D PS modelling to evaluation oil generation in Wichian Buri sub-basin
Authors C. Chaiyasart and P.H. GiaoSummaryThe Wichian Buri sub-basin of Phetchabun basin, Thailand is reported the significant recoverable hydrocarbon from fractured igneous rock reservoirs but until now no detailed research has been done to estimate the hydrocarbon generation and intrusion effect to maturation. In this study, an integrated approach was proposed and applied both petroleum system modelling (PSM) and hydrocarbon generation to evaluate potential source rock of Wichian Buri unit IV with intrusion effect. The study was conducted base on the data from public domain of petroleum industry in Thailand, including vertical well sections, well logs, regional geological sections, base maps, and geochemical data. The results of petroleum system modelling (PSM) indicated that potential source rock in Unit IV was maturation and generate HC with the effect of igneous intrusion. The Ro of the source rock is 0.62% and hydrogen index of the source rock is 222 mgHC/gTOC. Hydrocarbon generation was found in the late Miocene basalt tertiary and Permo-Triassic Nam Duk formation. Finally, the hydrocarbon generation estimated 1,392.4 - 2,489.7 MMSTB of Wichian Buri unit IV and results of this study concluded that the igneous intrusion effect to immaturities source rock to generate hydrocarbon.
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a-Value and b-Value as Basic Calculation Seismicity Index, Repeated Period, and Vulnerability of Earthquakes
Authors A. Arimuko, F. Yoan, S. Rohadi and K. H. C. WulurSummarya-Value and b-Value can be used to basic calculation to get seismicity index, repeated period, and vulnerability of earthquakes in a region. Yogyakarta is a region of Indonesia that often earthquakes are happened, caused by an active fault it has, Opak fault. And also because it is flanked by Java Megathrust and an active volcano. Earthquake phenomenon is very detrimental to life and many casualties if there is no preparedness to deal with it. This research aims to get the calculation results from seismicity index, repeated period, and vulnerability of earthquakes to indicate areas prone of earthquakes in Yogyakarta. The method used is a matrix inverse calculation, Gutenberg-Richter’s (1956) least square equation, to obtain a-value and b-value. This research uses USGS and BMKG earthquake catalog data and classifies it based on the region of Yogyakarta in geodetic coordinates ie 7.493°-11.523°S and 109.841°-110.940°E. The results of this research is got a-value and b-value calculations in Yogyakarta are found a = 4.0866 and b = 0.6528. And from the calculation results obtained that the seismicity index, repeated period, and earthquake vulnerability that occurs is Mw ≥ 5 in Yogyakarta.
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Integrating Geophysics, Geology, and Geochemistry Methods for Shallow Biogenic Gas Exploration in Indonesia
Authors Z. Firdaus, R. Muammar and D. RalanarkoSummaryShallow biogenic gas has long known as a drilling hazard in petroleum industry which responsible for several blowouts in the past time. Despite its infamous name in the industry, biogenic gas usually composed of more than 95% methane and it contains considerable amount of global reserve to be produced in a relatively shallow area. In order to turn biogenic gas into a production horizon, different treatments are needed. This research took place in Bentu PSC, Talangjimar Field, and Tunu Field which are distributed in Central Sumatra Basin, South Sumatra Basin, and Kutai Basin respectively. By integrating AVO analysis (geophysics), burial history and geothermal gradient (geology), as well as carbon isotope and gas composition (geochemistry), one can easily detect the presence of biogenic gas in the subsurface area along with its origin and quality. Our investigation suggested that by combining the three geosciences elements, the chance of exploration success may increase significantly, leading to the addition of biogenic gas reserve to be produced in the future.
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The Influence of Focal Mechanism to the Tsunami Wave Height of the Simeulue Aceh Earthquake on April 11, 2012
Authors U.I. Nurdiana, F. Purnamasari and A. NurokhimSummaryEarthquake in Simeulue Aceh happened on April 11, 2012, at 08:39:31 GMT with latitude coordinates 2.35° and longitude 92.82° with magnitude 8.6 Mw. This earthquake occurred at a depth of 45.6 km. Because of this earthquake, the tsunami was recorded in several places. Meanwhile, a small tsunami reportedly hit the island of Simeulue that dragged objects to the coast and created 3 meters height waves in the Gulf of Sibigo, West Simeulue. The April 11, 2012 Simeulue Aceh earthquake was the largest earthquake caused by a strike-slip fault. This earthquake was categorized as an outer-rise quake because it was located outside the subduction zone. The April 11, 2012 Simeulue Aceh earthquake was dominated by horizontal (strike-slip) component, where the horizontal component was dominant, so it did not generate the large tsunami waves. The tsunami propagation models also different between the tsunami model without the focal mechanism and with the focal mechanism (we used strike 20 and 289). From 2 data station, Sabang and Nancowry validation result, then compared the observation result with IOC data, so we know that the height of tsunami was influenced by focal mechanism, in this case, the strike 289 is the nearly compatible with IOC data.
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Volumetric Calculation Based On Comparative Resistivity Imaging Analysis Between Marquadt And Occam Inversion: An Andesite Quarry Case Study
Authors Aditya Aries Furkhan, Agra Adipta and Wrego Seno GiamboroSummaryVolumetric determining in mining prospect encounters certain biases. Resistivity imaging was comprehended to determine the resistivity distribution of the andesite body. Inversion is used to characterize a subsurface properties upon the geological condition. Inversion data are transformed into model parameters which could explain the possible subsurface properties that may cause the data be obtained based on the acceptable forward formulation ( Martakusumah and Srigutomo, 2015 ). Marquadt and Occam inversion are non-linear inversions with a linear approximation. Both of inversions are used on the resistivity data resulting a comparative resistivity model. The result from Marquadt inversion suites more with the geological condition, in contrary with Occam inversion. Andesite body identified as a high resistivity value ranging 400 – 2000 Ω.m. Marquadt inversion portray intrusion shaped andesite with a volumetric reaching 9,987 x 106 m3.
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Surface deformation monitoring of Mt. Agung by Sentinel-1 DInSAR
SummaryPhreatic eruption occurred on November 21, 2017 on Mount Agung with the ash cloud reaching the height more than 3,800 meters. This was followed by multiple magmatic eruptions occurred since November 25 to 27. Volcanic activity has been weakened after November 29, but it is still continuing.
In this study, recent status of the surface deformation of Mt. Agung, detected by DInSAR using Sentinel-1 satellite data, is reported. Preliminary results indicate that no deformation occurs before the phreatic eruption, but after the eruption a swell on northern slope may occur.
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3D joint inversion of gravity and magnetic data based on structure similarity of node physical property model
Authors S. L. Li, N. P. Wang, X. H. Meng and J. WangSummaryThe node physical property model with good sparseness is the difference form of its corresponding block physical property model. It can not only eliminate computational redundancy and improve the efficiency of forward computation, but also can effectively recover simple geology models. The developed gravity-magnetic simultaneous inversion method introduces the structure similarity constraint between two node physical property models to make the inversion results have the characteristics of structural consistency. The Cauchy norm constraint can be used to get a sparse solution. Within the conventional inversion framework, this strategy does not need to apply nonlinear functions such as physical property transformation function to overcome the problem of nonlinear enhancement, and the inversion results are not affected by the initial value. The model tests show that the inversion method can effectively recover simple geology models. The boundary of the recovered anomalies is clear and the location is close to the real position. The block physical property values of the recovered anomalies are also closer to their true values. Compared with the inversion using only one geophysical method data, the joint inversion improves the vertical resolution of anomalies to a certain extent, and inhibits the generation of partial interference anomalies.
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Seismic Wave Modeling of Numerical Dispersion using Cross-rhombus Stencil
Authors A.D. Sonya and T.A. SannySummaryFinite difference is a popular method that used for seismic wave modelling, but it still suffer from numerical dispersion problem. Stencil is one of finite difference aspect that affect its accuracy, including the dispersion. Cross-rhombus stencil is a new stencil scheme which combine the standard stencil and a diamond-shaped stencil called rhombus stencil. It is proved that it can reduce numerical dispersion in finite difference method and increasing its efficiency. Since it is new scheme, cross-rhombus stencil has a lot of things to be studied. We described basic theory of this stencil scheme and its application to a simple seismic modeling simulation.
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Surveying the layers of pavement using ground-penetrating radar
Authors K. Onishi, H. Kisanuki, T. Ogahara and T. InazakiSummaryMulti-channel GPR with ground coupled antennas can acquire underground records with little amount of multiple reflections. We use multi-channel GPR equipment, which can scan at high speed on a paved road, to acquire underground survey records at a test road which has many sections composed of different type of materials and depths. The records clearly indicate horizontal boundaries of road construction without processing of background removal. We acquired zero-offset profiles applying normal moveout (NMO) correction for GPR records. NMO correction is useful to detect the shallow boundary below asphalt concreate mixture. GPR with bow-tie antenna of ground coupled type, which can scan on paved road at high speed has high potential to monitor the condition of road construction.
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Large 3D resistivity and IP measurement of the Séchilienne landslide using the FullWaver system
Authors C. Truffert, P. Nevers, M. Lajaunie, J.P. Malet, C. Bertrand, J. Gance and O. LeiteSummaryLa Séchilienne is a hudge deep seated landslide located in the French Alps. Authors will present a full 3D Electrical Resistivity Tomography (ERT) performed with the FullWaver(c) system designed by Iris Instruments. This distributed, autonomous and cable free solution allows to restitute a 3D distribution of resistivities useful for a better understanding of the geometry and the processes of the landslide.
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Paper Title for Landslide Identifications Based on Geology and Geoelectricity Mapping Analysis, Study Area: Road Province Pacitan-Ponorogo, East Java, Indonesia.
Authors L. R. Daryono, A. Hendratno, M. Nukman and E. HartantyoSummaryUnderstanding of landslide mechanism was imperative to appropriate the mitigation geotechnical methods. Engineering geological investigation and geoelectrical dipole-dipole resistivity analysis were carried out in the studied area to elucidate the mechanism of the landslide. The engineering geological investigation consists of local topographical mapping. The geoelectrical dipole-dipole resistivity analysis assessment of the problems affected landslide was conducted by a sub-surface imagine using resistivity contrast. The results presented in this paper successfully detect fractures at various depths and their position with the resistivity low contrasts as claystone is among the high-resistivity zones (volcanic rock). Low resistivity zone has a pattern with a slope of ∼45 degrees to the East and acted as field shear-surface the movement of soil in landscape survey. Interpretation of resolution lithology and shear-surface fields ranging between 25 – 30 m.
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Integrated Remote Sensing and Geological Mapping to Identify Landslide Prone Zone in Loano, Purworejo, Central Java
Authors I. D. Puta, A. Hirawan, R. Abbas and A. D. TitisariSummaryLandslide is one geological disaster with a high risk that often occurs in Central Java Province, including in the Loano Area, Purworejo District. .Today there are many people in Loano who dwell in areas prone to landslide. However, it is necessary to conduct integrative research activities as a form of disaster mitigation to reduce the landslide risk. Research conducted in the form of remote sensing, geological mapping and GIS (Geographic Information System) analysis. Remote sensing observation shows that the factors control the Landslide are the presence of non vegetation in the southeast and west side of the areas, the slope (<15O), less crystalline rocks, geological structure, and hydrothermal alteration minerals.The lithology is composed of 4 rock units: basaltic andesite, andesite, tuffaceous sandstone and andesite breccia. The alteration zone lies in the unit of andesite lava lithology. The various clay minerals minerals in the form of illite, smectite, and kaolinite are the result of hydrothermal alteration which can be classified as an argillic type. There are 10 points of landslide prone zone. The zone is characterized by a slope above 15o and a high alteration level. Highfall rate of rainfall (131 – 241mm/month) in Kulonprogo area also believed control the landslide.
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Identification of Landslide Vulnerability Using Seismic Refraction and MASW: Study Case in Kulonprogo, Indonesia
Authors H. S. Mahandani, K. S. Brotopuspito and A. AnggrainiSummaryResearch on landslides has been done in Purwosari Village, Girimulyo Sub-district, Kulonprogo Regency with Seismic Refraction and MASW’s methods. The study consists of 20 Seismic lines to determine the level of landslide vulnerability in the researh area. Vp and Vs values obtained are then used for calculating the elastic properties of rocks in the weathered layers. Result of the analysis shows that the most vulnerable area of landslides is in District of Gedong in Purwosari Village which is located in North-West of the research area. This area has a low Vp, Vs, density, Shear and Young’s Moduli with high Poisson’s ratio indicates that the area is water saturated. Water saturated slope will have lower frictional force that makes the weathered layer prone to landslide.
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Estimation of Aquifer Properties Using Surface Based Electrical Resistivity Tomography
Authors T. Fadilah, L. Gross and R. SchaaSummaryAquifer characterization such as hydraulic conductivity (K) is necessary due to groundwater sustainability for agriculture industry. The current method for calculating K is to conduct a pumping test or a permeability test. This study is trying to find an alternative method to obtain a K value by determining the correlation between water and aquifer resistivity which is conducted in the laboratory and field scale. The aquifer resistivity is gathered from Electrical Resistivity Tomography (ERT) and the water resistivity from direct measurement. The correlation can perform the Kozeny–Carman equation, which is modified from Archie and Waxman–Smits formulas, to estimate the hydraulic conductivity. The hydraulic conductivity estimation is compared with the hydraulic conductivity value from the permeability and pumping test solutions. The measurement result showed 12.63 m/day, which was similar to the permeability test with 10.3 m/day. However, the field result revealed 14.07 m/day, while the pumping test indicated 24.5 m/day. An analysis has been conducted with the fact that geological condition, grain size, and water resistivity have a significant contribution to the result. Nevertheless, the outcome of the ERT profile can be an alternative method to get an estimation of K that is more efficient, yet not offensive.
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Resistivity Method with Werner-Schlumberger Configuration to Analysis Seawater Intrusion at Teluk Betung Area, Lampung
Authors Taufiq, H.D. Mega and A. ZaenudinSummaryTeluk Betung area is an area in the southern coastal of Bandar Lampung city directly adjacent to the sea. Based on a survey of residents wells in the area, indicating that the groundwater in this area has been contaminated by seawater (brackish) so it is not suitable for consumption. This occurs because of the increased need for fresh water in proportion to increase of population in the region resulting in ground water exploitation continues to increase every years. The reduced water content in the soil may result in the entry of the aquifer layer of seawater into the aquifer zone and contaminate ground water, this condition is often referred to as seawater intrusion. To mapping the pollution zone caused by the seawater intrusion we used resistivity method.
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The Groundwater Survey by using Resistivity Method and its Application in the Republic of Rwanda
Authors K. Nakamura, T. Aizawa and S. MatsudaSummaryThis paper presents result of the groundwater survey by using resistivity method and its application especially in the developing countries based on the lessons learnt through the feasibility study of irrigation facility rehabilitation project in Republic of Rwanda in eastern Africa.
As a result of the study, the water catchment structure was examined by resistivity survey, and availability of water resource was also confirmed. In addition, it was confirmed that the interpretation of the resistivity survey results for the water catchment structure in the laterite soil of this country is appropriate. This suggests that there is sufficient possibility of project cost reduction due to early implementation of resistivity survey. In the future, it is considered that similar interpretations can be made in the case of constructing an alternative water facility in the vicinity of a place already having a spring as in this time.
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Search for and investigation of volcanoes with gravity surveys
By J. MrlinaSummaryGeophysical methods, mainly gravimetry and magnetometry, can serve as suitable tools for location of unknown hidden volcanic structures that are not expressed by any typical topographic features. These may be e.g. diatremes and maars with eroded scoria cones or rims of tuff/tephra material, as well as lava flows.
Gravity survey may reveal significant negative anomalies due to low density of the filling of volcanic vents, or positive anomalies over the bodies of compact lava accumulation. Magnetometry would rather show positive anomalies related to most of the volcanic structures due to high content of magnetic minerals in the volcanic rocks (except acid trachytes/phonolites/rhyolites). Geophysical surveys should therefore form part of any investigation of volcanic fields where some unknown volcanoes may still be expected.
Gravity monitoring can reveal hidden mass and fluids movement in a volcano interior, and can therefore contribute to the hazard control at regions with active volcanoes.
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Seismic Lahar Characteristics of Merapi Volcano Post 2010 Eruption
Authors Sulistiyani, IGM. A. Nandaka and NurudinSummaryMerapi 2010 eruption ejected at least 130 million m3 volcanic material, mostly enter to Gendol River. More than 100 lahar events were generated around Merapi. Lahar at Merapi triggered by the rain intensity occurred at the summit. BPPTKG built the lahar flow monitoring station in order to mitigate the lahar disaster. The intention was to give early warning to the society. Lahar flows monitored using non-contact detection instrumentations installed near the rivers. These devices were geophones and IP-based camera.
This paper will present the seismic lahar characteristics recorded at Kali Gendol station. Events recorded on February 21, 28, April 23, 24 and also May 1, 2011, has been analyzed to know the characteristics. Most of the data had saturated amplitude due to the big magnitude lahar caused by the blocky materials. Seismic signal shows that the flow can be differentiated into single-pulse and multi-pulse events. Dominant frequency before the arriving of the lahar was fluctuating because of the human activity, traffic, etc., while the body of the lahar was 8–18 Hz. Maximum amplitude ranged between 1x104 – 1.9x104 Count (saturated). By knowing these lahar characteristics, amplitude and frequency result can also be used to refining the lahar early warning system.
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Hypocenters Relocation Using Double Difference Method Around Mount Agung, Bali
Authors E. Ulfiana and R. M. SipayungSummaryAfter a long sleep for 54 years, now we are surprised by the presence of seismic activities of Mount Agung that has recorded since September 2017. We can’t prevent the eruption, however we can observe magma movement in the body of volcanos. Hypocenters distribution is an important information that can be used to reveal the magma movement in the body of volcano. For a more accurate hypocenter, we did relocation of earthquake hypocenter that has occured in Mount Agung area, periode September–November 2017 (Catalog data from BMKG). We used Double Difference method that compute in HypoDD program. We success relocated 331 from 415 events that occured since September-November 2017 in Mount Agung area. The hypocenter distribution looks more accurate and earthquakes are located under Mount Agung with range depths 3–42 km. The dominant hypocenter distribution lies to the southwest of Mount Agung, ie toward the middle between Mount Agung and Mount Batur. Magma is going move toward the surface or in brittle zones of Mount Agung. The small eruption has occured in Mount Agung, so we expected a higher probabilty for a large eruption can be occure following these small eruptions.
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Spectra analysis for source dynamic identification of deep volcano tectonic underneath mounth Sinabung, North Sumatera
Authors K. Brotopuspito, T. Kusmita and H. TriastutySummarySpectra frequency of VT indicates the effective stress of volcanic activity. Spectra frequency of VT indicates the effective stress of volcanic activity. These spectra parameters could be applied to determine source and the dynamics of the source of the VT earthquake. This study analyzed the spectra VTA earthquake in the Sinabung volcano between July and November 2013, by applying the FFT algorithm based on the Brune model. Analysis show that the corner frequency of VTA earthquakes of Sinabung volcano were dominated by frequency of 12 – 13 Hz. Hypocenter positions were at a depth of 2 km - 20 km from the summit. Epicenter positions were spread towards the Northwest from the summit, i.e to the Lake Kawar direction. Most of the VTA source mechanisms are strike slip and oblique, and small portion of normal faults and reverse faults. Energy accumulation before the eruption was occurred from July to August and after eruptions in October. On this October accompanied by the formation of a new dome and followed by a magmatic eruption in November. Fractures that triggered the eruption was happened on September 12nd, 2013 and ended on September 22nd.
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Identification of Distribution and Calculation of Manganese Reserves from VLF and IP Method in Pengasih, Yogyakarta
More LessSummaryResearch about manganese reserves has been done in the Karangsari Village, Pengasih District, Kulonprogo Special Region of Yogyakarta. Explorations and exploitation of manganese has been done by local community using traditional method. This research aims to determine the condition of subsurface, manganese distribution, and the amount of manganese reserve in research area. The method used is VLF method and IP method. The line of VLF measurement is 6 line with 300 m length. IP line using dipole-dipole configuration has 5 lines and 300 m length, spacing between electrode 20 m and number n 8. The aquisition using T-VLF BGRM IRISH instrument and Syscal Jr. Resistivity meter. The result of the research is the distribution of manganese in resistivity< 40 ohm.m and chargeability< 10 msec. The range is used for 3D modeling and manganese volume of 228,000 m3. The manganese reserve of the research area is 984,960 ton
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3D ERT/IP Imaging for Sulfide Mineralization over Proterozoic metavolcanics in Dhanjori Basin, Eastern Singhbhum, India
Authors A. K. Gupta, S. Srivastava and R. K. SinghSummaryThe study area, Paleoproterozoic metavolcanics in Dhanjori Basin, Eastern Singhbhum, India, is the rich source of gold associated with sulfide, quartzite veins and Quartz Pebble Conglomerate. ICP-AES analysis of samples from the study area reported the average concentration of gold, silver, copper, uranium, magnetite, lead and zinc as 5ppm, trace, 110 ppm, 50 ppm, 1.5 ppm, 6.5 ppm and 55 ppm respectively. A regional audiomagnetotellurics (AMT) study in the region indicated the presence of shallow conducting heterogeneities. This study presents the results of 3D Electrical resistivity tomography (ERT)/Induced Polarization (IP) surveys for detection of sulfide mineralization over one of these conductors identified from AMT study. The inverted model shows conducting and moderately chargeable zone as a weathered cover shallow aquifers up to 20 m depth. However, for depths more than 20 m, the lithology is broadly resistive with few conductors of small dimensions surrounding it. These are distinguished on the basis of chargeability variations from low (6mV/V) to high (90 mV/V) indicating distinct geological features such as massive sulfide, QPC/quartz vein with disseminated sulfide gold, greenstone schist, and dolerite dike/Proterozoic gabbro anorthosite mass. The future scout drilling program has been concentrated on the identified zones of sulfide mineralization.
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Manganese Mineral Exploration in Kulon Progo District Using Induced Polarisation Method
Authors G. Erlangga, I. Arifianto and K. AfafaSummaryKliripan and Anjir Sub-village, Kulon Progo district were known as one of big manganese mining in Java island, but a big scale mining on the surface is uneconomic anymore. Based on the geological setting, there is a chance to discover a new deposit resource in the subsurface. Therefore, manganese exploration using induced polarisation method had been done in this area. Data acquisition was obtained by utilizing Syscal Jr. with 10 – 20 meter electrode spacing, and n=6. The data was processed to delineate a prospect zone of manganese mineralisation. Resistivity and chargeability of manganese are considered in the interpretation. Mineralisation zones of manganese are clearly seen at the second and third line. From the reference, manganese minerals have a 135 – 250 msec chargeability value. On the second line, the mineralized zone is located at 65 meters above sea level and distance of 250 meters on section line. While mineralisation zone in the third line is located at 70 meters above sea level and a distance of 110 meters on the section line, both of them are at Anjir Sub-village. The mineralisation zone is guessed potential as a manganese hill associate with limestone deposit, refer to the outcrop at surface.
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Remote Sensing Application in Exploration of Iron Mineral Placer Deposit: Case Study of Kulonprogo’s Iron Placer Deposit
Authors I. D. Putra, R. Abbas, S. D. Masti and I. W. WarmadaSummaryIndonesia is a country of Island arcs setting, tectonically. This setting has induced many of volcanoes Indonesia followed by the presence of mineral deposits. As the consequences of never-ending demand for ore minerals, exploration of mineral deposits are always needed. The study area is located in Kulonprogo, Yogyakarta. The study area is marked by secondary type mineral deposit presence of Placer type. Several band combinations analysis of Landsat 8 OLI/ TIRS 432, 567, and rationing of band 5/6 and 4/2 are done as methods in order to reveal the geological, and geomorphological conditions of the study area and the dissemination of iron-bearing mineral in the source and in the secondary deposit. The result of the analysis is the dissemination of the iron-bearing mineral are present covered wide area within and around the Glagah beach, the iron mineral source are located several kilometers to the north, the transportation of iron-bearing mineral is done through fluvial mechanisms of Serang and the other River to the beaches in the south. Some factors are also expected to affect the deposition processes, such as mineral density, waves, and river’s current speed. From this study, it’s believed that remote sensing is useful “tool” in mineral exploration.
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The Potential Development of Rajabasa Geothermal Manifestations in Kalianda Into Geoturism Area in South Lampung
Authors M. Addiansyah, R.D. Linggadipura, A. Krestanu and M.H. PrasetyoSummaryKalianda has very interesting geological phenomena that evidenced by the existence a several manifestations of Mount Rajabasa Geothermal System those became the research object of geoturism area development. The research methods are field observation, studio analysis, and quantitative analysis of geosite and geomorphosite based on Kubalikova (2013 ) to assess the development potential of Kalianda into geoturism area. Parameters of quantitative analysis of geosite and geomorphosite that used are scientific and intrinsic value, educational value, economic value, conservation value, and additional value. Based on the results of field observation and quantitative assessment towards geological objects located in Kalianda and surrounding area, six geological objects that are potential to become geosites and geomorphosite. Those are Rajabasa Volcanic 65.1%, Maribung Waterfall 46.6%, Way Kunjir Geyser and Hot Spring 45.9%, Wartawan Beach 72.5%, Belerang Simpur Hot Spring 66.6%, and Way Belerang Hot Spring 65.2%. Those data indicate that Kalianda Area has potential to become geotourism area geoscience field campus with volcanology, geothermal, and oceanography learning aspects. In order to optimize the operational geoturism area needs to be equipped with cleanliness facilities, lodging, and scientific sign board. Kalianda Geoturism Area development is believed will improve the economy of the community around Kalianda Area.
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Estimation of average electromagnetic wave velocity in tree trunks for the reflection imaging by GPR
Authors K. Takahashi and K. AoikeSummaryWe developed a simple method to estimate average propagation velocity of electromagnetic waves in tree trunks. The method employs GPR transmission measurements that fixes the transmitting antenna and scans receiving antenna circumferentially on the perimeter of a trunk. The data exhibit an arrival time curve since the measurement configuration consists of various propagation lengths. We modified the velocity analysis of CMP measurement and calculate semblance as a function of relative permittivity (or velocity). The maximum semblance indicates the permittivity value that best describes the arrival time curve in the transmission data and the value is the estimation. We demonstrate the method with a laboratory experiment with a drilled log and that the estimated permittivity gives better reflection image than other values.
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Earth Material as Supporting Tool in Legal Case Investigation and the Role of Geoscientist in Disclosing the Criminal
More LessSummaryForensic geology is defined as the application of earth science in the field of law (Munroe, 2002). Forensic geology to date still sounds foreign, especially in Indonesia. Whereas the application of forensic geology can be a reinforcement tool in law enforcement processes. The background of the use of earth’s material as an instrument of investigation is the variety of materials of this earth, such as soil, lithology, minerals, fossils. The diversity ranging from physical, biological to chemical, such as size, color, shape, composition, and mineralogy. In this modern era, tools have been able to identify such materials as using polarization microscopes for microscopic observation. Another thing that underlies the application of forensic geology is the assumption that any contact with the earth’s material will result in a trace of the perpetrator, the victim, the object, or the scene of the case which then identified the material, its origin, similarities with other areas, and so on. This becomes a great potential in the law enforcement process, and becomes a supporting tool to unravel the mystery of the criminals. Here the geoscientist’s role is needed to identify and observe the earth’s material and Indonesia has many reliable geoscientist to solve the problem.
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Merangin Paleobotany Park: Geological Aspects and Characteristics
More LessSummaryIndonesia with its complex tectonic structure are gifted by abundant resources spreading along its archipelagos in both biological and geological resources, in terms of landscapes, fossils, rocks, and other geological aspects. Geopark as a product of these setup are now intensively developed in Indonesia as well as other countries. One of well-known geoparks in Indonesia is Merangin Geopark that administratively located in four regencies, including Merangin Regency, Kerinci, Sarolangun, and West Tanjung Jabung. This geopark is mostly acknowledged for its finding fossils and geological landscapes that have a high scientific value in terms of geology for scholars interested in studies related to the earth formation history for education and research purposes. Focusing in geological condition of Merangin Paelobotany Park as a core region of Geopark Merangin, this study can be utilized as a comprehensive study to enlarge the references regarding the geological condition in this study area. There are at least 18 geosites available in this area, consists of diverse morphology, such as lakes, caves, rivers, underground rivers, waterfalls, and mountain; unique geological structures; variety of rock types; and Araucarioxylon wood fossil as the icon of Merangin Geopark with other various fossils - plant roots, trunks, leaves, and marine animals.
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Conductivity-depth imaging of semi-airborne transient electromagnetic data
Authors X. B. Wang and X. D. YuSummaryConductivity-depth imaging is a common method for the interpretation of airborne transient electromagnetic data. The interpretation of Semi-airborne transient electromagnetic data is similar to the airborne transient electromagnetic method, due to the large amount of data, the similar imaging method is also required. In this paper we present a SATEM CDI method which based on nonlinear implicit function, and use one field data to verify the practicability of this method, and we also compared the CDI results with the geological information and ground inversion results. The results demonstrate that this CDI method is practical for SATEM data.
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Magnetotelluric 1D Inversion Using Grid-Search and Monte Carlo Methods
Authors S. Maulinadya and H. GrandisSummaryThe magnetotelluric (MT) 1D inversion modeling is relatively simple and can be considered as a solved problem. Nevertheless, this subject still attracts researchers to study further for its nonlinearity, equivalence and usefulness for particular situation. For example, in the preliminary stage of a geothermal exploration program, 1D MT modeling is still employed to obtain an overall view of the subsurface resistivity distribution in the prospect area. Another example is the regional study of basement structures where the filling sediments are mostly stratified. From the
computational point of view, the nonlinear, gradient-free approaches to the inverse problems are gaining interest due to the availability of powerful computational resources. The paper describes the 1D MT inverse problem resolution using grid-search and Monte Carlo approach. The “a priori” information is set to define the model space or search area. The grid-search attempts to search for the solution by evaluation of all possible models contained in the model space. The Monte Carlo approach is used to reduce the execution time using random samples from the model space. Tests
using synthetic and field data associated with simple synthetic models showed satisfactory results, in terms of model recovery and misfit.
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Near surface passive seismic HVSR surveying for mineral exploration, regolith mapping and other applications
Authors D. Stannard and J. MeyersSummaryA presentation highlighting the application of the HVSR passive seismic technique to assist with regolith and basin thickness mapping for exploration of mineral deposits, shallow sedimentary basin mapping and shallow quarry materials. Several case studies from passive seismic surveys carried out by Resource Potentials using the Tromino seismometers will be presented to highlight some of the potential applications of this technique for widespread exploration throughout Indonesia and SE Asia.
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IP-Resistivity for shallow gold exploration. Case Study: “UBITS” block, Pohuwato District, Gorontalo Province.
Authors V. A. Prasetyo, P.R. Aripin, A. Ismanto and M. E. C. LubisSummaryIP-Resistivity method has been conducted for shallow gold exploration in UBITS block, Pohuwato District, Gorontalo Province. The occurence of gold mineralization linked to low sulphidation system. From the 2D section the high chargeability and high resistivity are the two vectors for gold mineralization zone.
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Investigation of the Structural Controlled Mineralization: Integrated Geology, Geophysics and Remote Sensing in Kulonprogo
Authors B. B. Prabowo, V. P. Harefa, S. E. Senduk, A. A. E. Wowor, Y. D. Tae and R. R. SeranSummaryThe Kuloprogo high is also a fairly complex area of alteration and mineralization. A study of geological structures at Kulonprogo high was conducted to determine the structural control of alteration and mineralization and further investigation of the potential availability of valuable metal minerals in the area. The study was conducted with alignment interpretation through Remote Sensing Geology, Geophysics and measurement of geological structure data.
In the result of the research. The presence of the mineralization is controlled by two tectonic phases that develop in the area. This is evidenced from geological mapping and alteration where the acquisition of mineral alterations that characterize the presence of mineralization. Hydrothermal alteration in the research area is silicification, argillic and prophylitic. Based on the characteristics of alteration and mineralization, the study area is included in low sulfidation epithermal type. It also appears on the Remote Sensing results where the targeted mineral distribution to be searched shows the distribution patterns trending to the structures geology that develop in the area. And from geophysical data showing a destructive magnetite pattern following along the structural zone as an accumulated container of gold and base metal.
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Characterization of Microtremor for The Identification of Subsurface Rivers at Kedung Banteng, Pacitan, Indonesia
Authors P. Chemistra, A. S. Bahri, W. Utama and A. WidodoSummaryHas been conducted research of microtremor characterization based on analysis of curves HVSR, particle motion, and time frequency analysis at Kedung Banteng river system, Pacitan, East Java, Indonesia to identify subsurface rivers using these characters. From particle motion data processing on 12 points of microtremor measurements, in area I, which is a river area, the resultant direction of point TA8, TA9, TA10, and TA13 is NW-SE due to the position of points that is parallel to the stream flow with E-W direction. It can be concluded two things. First, river can be the source of vibration to the point of measurement. Second, direction of particle is perpendicular to the direction of river flow.
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Utilizing Oil and Gas Industry Data to Understand Deeply Tarakan Earthquake
Authors H. Indrajaya, T.K. Usman and S. NuratmajaSummaryDuring this time people consider that the island of Kalimantan is a relatively safe area of the earthquake, but in fact it is not. One example is the earthquake that occurred in Tarakan. It happens in 2015 and 2017. Losses in the form of seven homes damaged but no casualties. The Tarakan region is located in North Kalimantan where the region is located in a compression zone caused by the Mangkalihat and Sampoerna Faults movement resulting in a wrench fault system. Given the data commonly used by Pertamina EP in constructing a subsurface model in oil and gas discovery combined with earthquake data it is hoped it will be easier to understand Tarakan earthquake which has been going on for two years. Three things will be examined in this paper to understand the characteristics of the Tarakan earthquake, which are earthquake active faults, the type of lithology surrounding epicenter earthquakes, and high stress areas.
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Determining Groundwater Recharge Potential Zone in Yogyakarta: Remote Sensing and GIS Approach
Authors A.S. Banuzaki, L.H.K. Pratiwi, G. Ikhwanushova and A. SetiantoSummaryYogyakarta is one of most-populated provinces in Indonesia having a high groundwater utilization. Most of water usages are still derived from groundwater resource. This condition is exacerbated by urbanization process which has a big deal on decreasing recharge area of groundwater due to land use change. To understand the water balance and the vulnerability of groundwater in Yogyakarta, the recharge area of groundwater need to be analyzed. The quantifying of recharge potential zone in Yogyakarta, was conducted by the integration of all factors influencing the hydrogeological process, those are lithology, land cover/land use, lineament and drainage frequency density, and geomorphology. The data were gained from satellite images (DEM and Landsat 8) and other exogenetic data (geomorphologic and geologic map). A GIS approach was used to integrate each influencing factor which has its own degree of effect. The groundwater recharge potential zone in Yogyakarta is well estimated using this method.
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Comparison of Transient Electromagnetic and DC Resistivity for aquifer layer in Cisarua, Bandung Barat Regency
Authors A. Laesanpura, D. Dahrin, W. Warsa, W.W. Parnadi, D. Abdurrahman, I.B.S Yogi and R. MarthenSummaryGeophysical investigation is conducted to study groundwater in water absorption region for Bandung Basin hydrology system. It is placed in Cisarua, Bandung Barat Regency, which composed of old and young volcanic products. Resistivity based geophysical methods are used, Geoelectrical Resistivity and Transient Electromagnetic (TEM). TEM measurement are usingused long grounded wire configuration with transmitter length 500 m and current 13 A. Geoelectrical Resistivity are usingused Wenner-Schlumberger configuration with maximum array distance 560 m. TEM Measurement recorded high amount of cultural noise since it is was near to cellular and radio transmitters. After filtering and inversion process, low resistivity zone (35–40 Ωm) are were detected at elevation 1185–1075 m. Deeper low resistivity zone assumed to have high water saturation are were also detected at 210 – -290m. This resultsed are were correspond with Geoelectrical Resistivity measurement which detecteddetect low resistivity zone at 1185 – 1140 m, with lowest resistivity value was 32 Ωm. In Geoelectrical Resistivity Section, we can could see that the low resistivity zone is was continuous from north to south. From both methods, the low resistivity zone are were interpreted as shallow unconfined aquifer serve as water source for domestic well in study zone.
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Integration of High Resolution Geoelectrical Resistivity and Refraction Seismic Profiling for Exploration of Groundwater
Authors S.C.H. Lee, A.G. Rafek and M.N.A. ZakariahSummaryThis paper presents the integration of high resolution geoelectrical resistivity and seismic refraction profiling for exploration of groundwater: case history from Chemor, Perak, Malaysia. The survey line is conducted at the intersection of two major faults where it is suspected to detect potential aquifers in limestone hardrock along the major fractures. Seismic refraction survey is used to determine the velocity of energy transmitted through the rock. Geoelectrical resistivity survey involved the use of new electrodes arrangement and sequence of measurements for Wenner-Schlumberger array and Dipole-Dipole array for geophysical field data acquisition in order to increase its data density and sensitivity to obtain high resolution 2-D subsurface imaging. The parameters that were taken into consideration while choosing the two most suitable arrays to be used were their sensitivity to vertical boundary, signal strength and total number of datum points. Data Levels Synthesization (DLS) technique also developed which involved the merging of data levels and datum points of Dipole-Dipole array and Wenner-Schlumberger array during resistivity data processing stage. DLS technique has effectively produced a high resolution 2-D geoelectrical resistivity image with enhanced horizontal and vertical resolution.
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A viable eco-friendly solution to meet India’s growing energy needs
By S.K. SharmaSummaryGeothermal reservoirs in India are of low to medium enthalpy type where surface temperatures vary from 80 to 105°C thus requiring a Binary Power Plant to convert their geothermal energy into electricity. Such generation of electricity through geothermal resource is preferable due to its eco-friendly nature whereas much environmental hazards are associated with the coal and nuclear projects.
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Prediction of Caprock and Structure of Candi Gedongsongo Geothermal System from AMT Data
Authors N. Alviandari, Yatini, F. Sulistyo, A. Suprobo, M. Rizki, B. T. Baihaqi and T. Y. YudhantoSummaryGeophysical investigation with AMT method conducted based on the existence of the surface manifestations on Candi Gedongsongo area and appear to identify the structure of the suspected fault as a weak zone both as recharge area and the emergence of the manifestation zone. This investigation was done on the post volcanic belt of older subduction zone that have significant geothermal gradient by the depth AMT data acquisition was done with Stratagem Unit 26716–01 Rev D by Geometrics that calculate true resistivity with its inversion then modeled on 2D model to identify the fault structure and 3D model to shows the caprock geometry. As a result there are 2 faults shows that has strike and dip of N350oE / 60o that continues from north to south and the second fault shown on P1 but the strike and dip can not be known. The caprock identified on high resistivity value ranges between 1000 -100,000 ohm.m with andesite lithology lying under elevation of 1000 m.
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Magnetotelluric Phase Tensor Application to Geothemal Modeling
More LessSummaryPhase tensor analysis generate invariant parameters such as the ellipticity (Φmax and Φmin) and slope angle of phase tensor (β) determine the dimensionality of the impedance tensor. If the structure of 1-D, then Φmax and Φmin will be equal, so the phase tensor form will be a circle with β is zero or near zero, for structur of 2-D the value Φmax ≠ Φmin while β is still zero or near zero and for 3D structure all components in tensor each impedance has a value and β ≠ 0 with a value of β< 3°. The results of the above phase tensor analysis show that the 1-D and 2-D structures are shown at frequencies of 320 Hz to 0.2 Hz (the period of 0.003 1s to 5.4s) and 3-D structures are shown at less from frequencies 0.11 Hz (period 9.588s). If the graphical representation non-symmetrical ellipse 2-D to the ellipse axis this because β ≠ 0, so it needs to be rotated to the ellipse axis with the angular value generated by calculation of α-β is -10o.
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Geology, Geochemistry and Geophysics of Guci Geothermal Prospect Area, Central Java.
Authors E. Gaffar, H. Permana, Y. Sudrajat, S. Indarto, H. Bakti and H. NurohmanSummaryGeothermal exploration have conducted in the Guci area. The methods were geology, geochemistry, geophysics and Radon. The Slamet Mountain Complex activity is controlled by the straight-line structure of the northwest - southeast, southwest - northeast direction of the main structure. The straightness of the northwest - southeast trending structures generally controls the activity of the old Mount Slamet or the Mingkrik Complex whereas the young volcanic activity is controlled by the southwest – northeast direction.
Areas which indicate Radon content can be interpreted that areas with low permeability, medium (Kalipedes), and high (Guci) are the areas passed by fault section. The radon content measured in the Guci and Kalipedes areas is high-high enough, indicating high permeability - high enough, ie> 40 dpm / L
Type of hot water in the Guci area based on the content of Cl, SO4, and HCO3, Guci areas (GC) generally indicate the type of bicarbonate. Hot water in a Guci in a geothermal system is called an outflow.
Magnetoteluric measurement result can be seen that geothermal prospect area for Guci and surrounding area is at Mount Mingkrik area.
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Depth Prediction of Gravity Data by Using Continous Wavelet Transform
More LessSummaryNawangan-Tegalombo is one of the mineralization zone in Indonesia. The research area is located in Pacitan-East Java. The mineralization zone is described by gravity anomaly which is there high gravity anomaly in reserach area. The depth prediction of the mineralization zone is calculated by continous wavelet transform with Morlet and Doubechies as mother wavelet. The source depth of the research area is around 1 km.
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Mineralization System with Magnetic Method in Kluwih, Pacitan, Central Java
Authors Fatimah, Muh Isnanto, Vergillio Asqueli, Audi Tri Lavanto and Faisal SangajiSummaryOre minerals are found disseminated sulfide ore pyrite, arsenopyrite, chalcopyrite, enargite and malachite. From measurements of geomagnetic found high magnetic anomaly< 700 nT surrounded by a low magnetic values and form a circular pattern, it is an indication of the pattern of anomalies of the porphyry system that is closed by the argillic lithocap. Based on data integration of geological, geochemical and geophysical the mineralization in the Pacitan area in the interpretation were in the proximal part of the High Sulphidation and suspicion leads to the porphyry deposits are still covered by the lithocaps.
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Ground Magnetic Survey for Shallow Iron Ore Prospecting
Authors H. Grandis and P. SumintadirejaSummaryA ground magnetic survey was conducted to delineate the existence of iron boulders located at shallow depth covered by soils. Typically, iron ore resources prospecting is done along with the extraction activities by digging or excavating using heavy equipment (backhoe). The geophysical survey aimed to avoid such trial-and-error process was part of our institution’s community services in Pelaihari district, Tanah Laut regency, South Kalimantan province, Indonesia. The relatively simple data processing and analyses of magnetic data were performed by using standard tools, i.e. freely available software and modelling codes. Our results showed the effectiveness of the iron boulders prospecting by using the ground magnetic method.
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Integrated Gravity and AMT Survey in Exploration of Primary Tin Deposit
Authors K. Apriliyanthy and M. YunusSummaryAn integrated Geophysical survey are Gravity and AMT has been carried out in Bangka Island to make a delineation of granite that is thought to be the source of tin mineralization.
Gravity anomalies show a high density around the edge of the maps, this high anomaly coincide with metasediment. While the low anomaly is related with alteration zone that surrounded the medium anomaly, it is interpreted as granite.
AMT inversion show an anomaly that confirmed the existence of granite which high density and high resistivity. This is supported by the existence of the low resistivity and low density as kaolin alteration zone that surrounded the anomaly.
The two fault direction are shown by Gravity map and also evident in AMT data. Fault with the trend of NW-SE from Gravity map is coincide with AMT Section, there is a low resistivity contrast extended downward that looks like a fault. On the other side, the high resistivity and high density is highly probable a metasediment unit which is resistive and dense but slipped NE-SW as shown in the gravity map.
The Gravity and AMT surveys delineated the existence of potential of the primary tin deposit of the granite at Bangka Island.
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Analysis of Microzonation Seismic Vulnerability Index around Repaking Village, Boyolali, Central Java using HVSR Method
Authors S.A. Widita, M. Kurniado, M.A. Girash and T.M. IrnakaSummaryMicrozonation analysis for seismic vulnerability was aimed to map the earthquake-vulnerable area at Repaking village, Wonosegoro Sub-district, Boyolali region, Central Java. Seismic vulnerability microzonation was done to map the vulnerability of a region based on its ambient seismic wave. The processing method that was used in this study was Horizontal to Vertical Spectrum Ratio (HVSR) method. In this study, HVSR method was used to analyze the site effect parameter prior to the seismic vulnerability. The parameter refers to Sediment Thickness (H) and Seismic Vulnerability Index. Those parameters are defined by generating Natural frequency (Fo) and Amplification Factor (Ao). The output of this study is the distribution of seismic vulnerability, which can give information about the hazard consequences, particularly on earthquake events.
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Comprehensive Analysis of Microtremor data to identify potential landslide (Study Case: KM23 Ponorogo-Trenggalek Road)
Authors B. Ramadhany, S. Sungkono, A. Rohman, D.D. Warnana and S. LestariSummaryPrincipal component analysis from microtremor data can be used to identify the potential landslide with azimuth and dip correlation, also the principal component data is compared with soil vulnerability index based on the calculation.
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Successtivity of Frequency Ratio to Predict Landslide, Study Case Daerah Istimewa Yogyakarta and Surrounded Area
Authors L. H. K. Pratiwi, A. Setianto, Y. P. Nusantara and A. WarmanSummaryTo reduce landslide hazard’s damage potension, it’s necessary to do a mitigation by mapping the landslide susceptibility area. Frequency Ratio is still rarely to be applied in Indonesia. This research is made to shows the accuration rate of the frequency ratio method application in Indonesia, especially in the Special Region of Yogyakarta and Central Java, so it can be a renewal for landslide hazard mapping method in Indonesia, which can help the landslide hazard mitigation. Landslide occurance in Special Region of Yogyakarta and Central Java is controlled by triggering factors such as slope, lithology, distance from drainage, distance from geological strucure, precipitation, and landuse. The result of landslide hazard mapping in this area indicates that the most triggering factor is the slope factor, especially the steep slope. The validation of this landslide hazard map using frequency ratio method shows the accuration rate is about <80%, so this method is good to be applied to produce a landslide hazard map.
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Conditioning of Stratigraphic Forward Modelling Using Geostatistics
Authors B. B. Ramadhana, S. Tyson, V. Bianchi and F. ZhouSummaryThe combination of Stratigraphic Forward Modelling and geostatistical technique can be used to improve the quality and comprehensiveness of the sedimentary reservoir model then reduce the costly data collection procedures to understand the reservoirs. The Stratigraphic forward modelling (SFM) is a process-based method comprising s realistic complexities and heterogeneities of its subsurface sedimentary architecture and may be applied in generating an enhanced model where limited well and seismic data available. The proposed method in this study is to generate a large SFM-basin scale then identify a field-scale location within this and applying some relevant transformation factor that matches the field conceptual deposition. Grainsize distributions may be inferred from well logs and compared against the grain size model in the SFM. Set of differences or residuals can be analyzed spatially and modeled using geostatistical techniques. Adding the modeled residuals to the SFM grain size will ensure that the hard data is honored. It is expected that more reasonable and defendable model characterization can be generated along with the main co-existed uncertainties and risks that can be captured and analyzed. The proposed methodology will incorporate the best advantage of each technique: process-based method for geological realism and Geostatistic methods for data conditioning
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Seismic Surface Wave in Irregular Dispersive Medium
By J. SafaniSummaryThe use of seismic surface wave method in civil engineering applications (such as determination of locations of building and bridge foundations, railway and highway route) become common practice in recent years. It is because this method provides shear-wave velocity, a parameter that directly related to shear strength of the subsurface structure which is an important parameter in civil engineering. In this paper, we discussed accuracy of the surface wave method in identifying the subsurface structure having irregular dispersive characteristic. Numerical and field tests were presented. Results from the numerical and field tests showed excellent ability of the surface wave method in delineating the subsurface medium with irregular dispersive characteristic. Comparison of a field test to the borehole data confirmed the ability.
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Joint Inversion of Rayleigh-wave Dispersion Curve for Near-Surface S-Wave Velocity Estimation
Authors A. Rubaiyn, J. Safani and A. PriyonoSummaryThe most important step in surface wave method is inverting Rayleigh wave dispersion curve for near-surface shear-wave velocity estimation. Joint inversion of Rayleigh wave dispersion curve has been developed. We combine the advantages of two different optimization methods, the genetic algorithm (GA) and Occam’s Algorithm. First, we use GA with small number generation to get the possible output solution, then we improve the solution (shear-wave velocity and thickness of layer) using Occam’s algorithm. We use several synthetic models to show performance of the joint inversion. Numerical errors are shown to appraise the value accuracy inversion model. Inversion of the synthetic dispersion curves for the four layers model provides most accurate solution models with is 0.0005 % and is 0.001%. Whereas, that for the six layers model also presents accurate result with is 1.48% and is 12.51 %. These errors indicate that the accuracy apply successfully join inversion scheme and promising application of surface wave.
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Effect of variation of shallow Vs profile from the MCMC inversion to variability of nonlinear soil amplification
Authors Saifuddin and H. YamanakaSummaryIn this study, we discuss effects of an observational error of phase velocity on a shallow phase velocity profile from a numerical case. Uncertainty in S-wave velocity profile is obtained from inversion of the phase velocity using the Markov-Chain Monte Carlo. The uncertainty of S-wave velocity profile is used to estimate the variability of nonlinear soil amplification. Variability of linear amplification is also estimated as the comparison to the nonlinear one. We find that the nonlinear amplification has less variability than linear response because of decrease of shear modulus and the increase of damping in nonlinear amplification.
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A Comparison of Tele-seismic Receiver Function in the Different Geological Units in Central Java
Authors P. Ariyanto, M.S. Rosid, Syuhada and Y. JanuartiSummaryIn this study, we derived crustal properties and shear wave velocity structures from analysis of teleseismic receiver function using Neighbourhoods Algorithm in the different geological units in Central Java. The results present here are the estimates of shear wave velocity models beneath 6 stations and the model of thickness of layer each geological unit. We observed the Moho depth at Central Java is about 22 to 38 km. In southern Central Java, the receiver function indicate a middle crustal low velocity zone, as Merapi Lawu Anomaly (MLA). The conversion Ps phase of the subducting Indo-Australian Plate is observed at several station at around 8.0 to 10.0 s. Several station that show high complexity data of receiver function require further study. They include stations at Quaternary Volcanoes and The Central Deppresion Zone of Java.
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Converted-Wave Seismic Reflection as an Alternative Key to Unlock Near Surface Imaging
Authors M. Oktariena and W. TriyosoSummaryNear surface phenomenon, such as shallow soft soil and gas cloud, has been proven for years as one of the obstacle in geotechnical and petroleum industry. Present as the anomaly to its lithological surrounding, these phenomenon have a similar characteristic in which triggering an imaging quality degradation, especially captured in conventional seismic reflection. Conventional seismic reflection is widely applicable for a deep target imaging, but it’s not impossible to use for a shallow target purpose. Multicomponent seismic survey records conventional both PP-wave reflection and converted PS-wave reflection. Obtained from converted-wave seismic, the characteristic of S-Wave brings along its unique capability of only propagating in solid medium. Through synthetic model based on real velocity data, this research will unveil the ability of converted-wave seismic in assisting conventional seismic for imaging purpose. With the interest located in shallow depth, a different approach will be conducted to bring in the best feature of each seismic wave behavior. The result reveals a series of simple seismic attribute and post-stack seismic inversion just the right approach to handle the intermeshing characteristic of PP&PS seismic reflection. Reducing ambiguity of PP seismic, PS seismic provides a highly improved imaging even when it is a near surface phenomenon.
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Effect of Dipping Layer in Source Energy Distribution of Ambient Noise
By C. LinSummaryGeophysical methods are effective ways to investigate the landslide area. Among them, passive surface wave method is an effective and economic way to measure the shear wave velocity profile especially in large-scale deep-seated landslide case. The influence of topography and dipping layers in the results of it is still not clear. As a preliminary study, we firstly focus on the effect of dipping layers. 3D numerical simulations based on spectral element method were conducted to study the effect. Ambient noises were numerically simulated for 2D array Spatial Autocorrelation method (SPAC) and for 1D array Multichannel Analysis of Passive Surface Wave method (MAPS). According to the results, the bias between the experiment dispersion curve and the theoretical ones in the centre of the array mainly come from the non-uniform source energy distribution. The dispersion curves retrieve from MAPS is much sensitive to the effect than the one from SPAC. The source energy distribution altered by the dipping layers and the dominant azimuth of the source energy would be frequency dependent. A frequency dependent correction can be applied to MAPS but the solution for SPAC needs further study.
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3x3C Seismic’s Sensitivity Analysis on Near-Surface towards Full Waveform Inversion
Authors T. M Irnaka, R. Brossier and L. MétivierSummaryFull Waveform Inversion (FWI) is a high-resolution seismic imaging tool which has been intensively developed during the past decade. At the near surface scale, FWI faces several challenges including 3D acquisition deployment, a strong presence of elastic effects, relatively high attenuation effects, and difficulties to propagate high-frequency waves. In order to better characterize such shallow targets, one of the solutions is to take into account data from multi-component sources and receivers. In this study, we analyze the benefit of 3x3C seismic data: 3x3C seismic is an acquisition technique which contains three orthogonal directions of the source and three component receivers. Although 3x3C seismic is feasible in practice, the benefit of such data for FWI is still not clear. This research uses two different synthetic models to assess the interest of 3x3C seismic data through the construction and analysis of the sensitivity kernel of both P-wave and S-wave velocities for each wave type (P-wave, S-wave, and surface wave), and each component. The results show that 3x3C data provide complementary information on the kinematic, dynamic and polarization of the wave propagation, yielding a potentially better reconstruction of the subsurface properties.
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Geophysical Investigations in Groundwater and Local Site Effect for Geotechnic Application
Authors B. Nurdiyanto, A.D. Guntara, I. Suyanto, M. Nukman, Suherman, I. A. Yunandra, S. Pamungkas, F. Muin, S. Sabbeq and A. S. FadliSummaryEnvironmental and development potential risks occur during the construction process of Geothermal Power Plants (GPP) site, with the discovery of several groundwater manifestations that arise on the surface due to excavation and development activities. Electrical Resistivity Tomography, Vertical Electrical Sounding, seismic refraction and microtremor surveys have been done to investigate these risks. It was intended to identify the aquifer, to provide information about rock structure and dynamic characteristics of local geological conditions in favour of the necessary of geotechnical engineering. 3D modeling results based on ERT data, geological interpretation and seismic refraction tomography concluded that the aquifers are in the brecciated lava zone as water reservoir while the impermeable layer are lava and clay. Aquifer forms two unrelated channels on the surface on higher elevations and merges into one channel on lower elevation. From the results of microtremor analysis concluded that GPP site area has very low values of seismic vulnerability index and ground shear strain. This low value due to the its geological conditions which is composed by andesitic breccia material on the surface. The location of GPP site is relatively safe from earthquake shocks except at the location of LB-12, LB-11 and LB-05 until geotechnical engineering is done.
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N-SPT and Transverse Resistance Correlation Using SPT and Geoelectric Data in Gunung Anyar
Authors M. J. Gultom, G. Wiranda, D. D. Warnana, W. Lestari, F. Syaifuddin and J. P. G. N. RochmanSummaryTraditional geotechnical approach for identifying basement soil in construction usually done by using borehole method such as Standart Penetration Test (SPT). SPT measures the soil strength by counting the number of blow of the device for a standart penetration to happen. SPT method is very useful in general for measuring the soil strength of a point, but it faces some disadvantages and difficulties. So, thisresearch correlate the N-SPT and Transverse Resistivity of two borehole and two VES data obtained in Gunung Anyar Regency, Surabaya. The correlation shows a minimal error with correlation value of 0.9008 and 0.8199. This results may help further research for consideration of VES substituting traditional SPT method for geotechnical application.
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Quantitative thickness estimate of tectonically deformed coal using seismic amplitude and sequential Gaussian simulation
Authors T. Chen, T. Mukerji and X. WangSummaryThickness of tectonically-deformed-coal (TDC) is a very important factor affecting safe mining and coalbed methane production. Instead of producing a deterministic estimate, we use variogram-based sequential Gaussian simulation (SGS) and seismic amplitude to produce a probabilistic quantitative assessment of TDC thickness. First of all, we use well-measured thickness of coalbed in a mine to model the variograms. Then, we use variogram-based SGS to simulate 100 realizations of coalbed thickness for every seismic grid in the mining zone. After that, we use those realizations to isolate the TDC-related amplitudes from the observed seismic amplitudes with estimated thin-bed tuning coefficients. Finally, we transform the TDC-related amplitudes of every grid into TDC thicknesses with a fitted linear equation. Through analysing thickness distribution of TDC for every seismic grid, we produce a TDC thickness estimate of the mining zone as well as its corresponding probability and uncertainty. The results show that the proposed method can take advantage of the large-scale regional well-measured coalbed thickness and the small-scale local seismic amplitude to produce a high accuracy and reliable TDC-thickness estimate.
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Studying active faults by combing GPR images with morphotectonic and trenching results. Ulaanbaatar, Mongolia
Authors N. Tsend-Ayush, M. Bano, A. Schlupp, U. Munkhuu, B. Davaasambuu and B. ByambakhorolSummaryMost of the Mongolian population 1.5 million is concentrated around Ulaanbaatar (UB) capital city, which is the main political and economical centre of the country. Hence, the seismic hazard assessment is of first importance for the country. The seismic activity observed in the vicinity of UB city increased since 2005. Several active faults have been identified around UB city and, according to their length and morphology, they can produce earthquakes of magnitude Mw = 6.5–7.5. The paleoseismology is the science that involves the search of ancient traces of earthquakes in the surface layers. It relies on methods including: quantitative geomorphology, trenches and various dating methods. However, the fault geomorphology is often smoothed due to erosion processes and a low slip rate, and the exact location of the fault is thus hidden. In such a context, the Ground Penetrating Radar (GPR) method gives good and useful results before paleoseismological trenching and can help to characterize faults by identifying offsets of radar reflections and buried fluvial channel deposits.
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Mapping of Kendeng Thrust Active Fault in East Java using Magnetotelluric Method
Authors W. Lestari, A. Widodo, D. D. Warnana, F. Syaifuddin, W. Utama and J. P. G. N. RochmanSummaryJava Island which is located north of the meeting between the two plates, that is The Indo-Australian Plate and the Eurasian Plate have several tectonic faults, as a form of stress accommodation generated by adjacent subduction South. Tectonic fault is a local deformation zone accommodate the movement of the plates through the deep aseismic creeping as well as episodic earthquakes or creeping in more layers shallow. Several previous GPS studies in the Java Island region were conducted by focusing in a localized deformation study located around the main fault region. Information on the near-surface fault in East Java (Kendeng Zone) is the reason for obtaining geometry information and the location of the fault in the deeper zone so that this information can add data on the earthquake potential in Java for mitigation actions and spatial interests. This research is expected to produce comprehensive and more detailed information about the process of deformation of East Java’s subsurface structure from Northern to Southern region with Magnetotelurics Method (MT).
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Comparison of Particle Swarm Optimization, Genetic, and Dragonfly Algorithm to Invert Vertical Electrical Sounding
Authors I. Ramadhani, S. Sungkono and H. GrandisSummaryIn direct current (DC) sounding (VES) data, inversion technique is applied to obtain the electrical property (resistivity) of subsurface. Inversion of VES data is a non-linear problem. Therefore, non-linear inversion techniques are used in this research, i.e. Particle Swarm Optimization (PSO), Genetic Algorithm (GA), and Dragonfly Algorithm (DA). PSO and GA are frequently used by researchers to solve VES inversion problem. However, DA has never been applied for that problem. These algorithms combine the explorative (global search) and exploitative (local search) concepts to obtain global optimum solution. Initially these algorithms are tested for noise free and added synthetic data in order to assess their ability. In both synthetic data inversion result, these algorithms are able to obtain model parameters which are sufficiently close to true model. In convergence rate, PSO and GA tend to be exploitative (fast convergence rate), while DA tends to be explorative (low convergence rate). In field data, these algorithms are applied to identify the sediment layer in the dried lake area, around lake Ayamaru, Sorong, Papua. In inversion result, the sediment layer has the thickness and resistivity value repectively about 3.3 to 3.5 m of dried lake surface and 20–27 Ωm.
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Optimized perimeter arrays for 3D resistivity survey in urban areas: a comparison with standard L and Corner arrays
Authors F. M. Abdullah, M. H. Loke, M. Nawawi and K. AbdullahSummaryIn highly populated areas, the 3D resistivity surveys are limited by many physical obstructions and it is not possible to use normally implanted electrodes in a rectangular grid in such cases. Therefore, an alternative special 3D survey case is when the electrodes are confined to the perimeter of the survey area. Thus, many approaches have been proposed for such case. In this work, the performance of the optimized perimeter arrays and a new improvement of these arrays in case of adding the noisy-weight to the algorithm were demonstrated and compared with the conventional L and Corner arrays using two synthetic examples. the optimized perimeter arrays achieve better resolution and structure detectability than 'L and Corner' array. In addition, there is a slight improvement with the noise-weights optimized data set in terms of reflects a slightly higher resistivity values and lowest model misfit. It is noted that the horizontal resolution is better than the vertical resolution.
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The use of positivity constraints in 4-D ERT inversion
Authors M.H. Loke, P.B. Wilkinson, T. Dahlin, J.E. Chambers, S. Uhlemann and T. DijkstraSummaryTime-lapse resistivity surveys are used to monitor changes in the subsurface. In some situations, it is expected the resistivity will only decrease (or vice versa) with time. The 4-D ERT inversion technique includes a temporal smoothness constraint to ensure that the resistivity changes in a smooth manner with time. However, it does not directly constrain the direction of the temporal changes in the resistivity. In some cases, the time-lapse models might show an increase in the resistivity with time in parts of the inverse model where it is expected to only decrease based on other information. We modify the 4-D ERT inversion method to remove this artefact. We first use the standard 4-D ERT inversion algorithm to generate an initial model. If the resistivity is expected to decrease with time, for the model cells that show a resistivity increase a truncation procedure is used where the resistivities of the different time models are reset to the mean value. The method of transformations is then used to ensure that the resistivities of the later time models are always less than the first model. The constraints can be applied to selected regions in the model in cases where additional information is available.
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Case study of crosshole GPR tomography for grouting distribution in rock fractures
Authors S. Bazin, Y. Kvistedal, H. Anschütz, L. Tunbridge, P. Jankowski, K. Fannian, H. Strømsvik and E. GrøvSummaryThe Nordic method for tunnelling consists of drill and blast, pre-grouting and rock support adapted to the geologic conditions. Extensive use of pre-grouting is normally applied to limit water leakage. The injection is stopped at a predetermined pressure or total volume of injected grout ( Stille, 2015 ). However, little is known about the dissemination of the grout within the host rock. The aim of this project is to better understand the grouting distribution in the fractures. The research is associated with the research program True Improvement in Grouting High pressure Technology for tunnelling (TIGHT) funded by the Norwegian research council. The objective of TIGHT is to increase understanding and subsequently implement efficient grouting control in tunnelling. The ultimate purpose is to reduce material consumption and time spent for grouting.
Geophysical instrumentation was developed to carry a crosshole Ground Penetration Radar (GPR) investigation in a pre-grouted tunnel wall. The GPR tomography results have been compared to the data recorded in the drilled cores. Preliminary results indicate that crosshole GPR can provide valuable information on the distribution of fractures filled with grout or filled with water.
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Through-Bit Logging
By S. MessamahSummaryBorehole geophysical logging tools are widely accepted as an aid to formation and resource evaluation. Nowadays, more often than not, the logging of drilled boreholes has become a mandatory requirement be it in exploration, reconnaissance drilling, groundwater or geotechnics. However, for a borehole to be logged, it needs to be accessible to the logging sondes and carry a minimal risk to their recovery. Accessibility can be an issue for example in highly deviated boreholes or in boreholes that are prone to collapse, blocking access or trapping sondes. In boreholes that present such access difficulties, a conventional wireline logging operation becomes either risky, difficult to perform or simply unpracticable. In these instances, suitable tooling and equipment can be deployed to allow for Through -Bit Logging (TBL) while tripping out pipe. The Geovista TBL technique has proved to be both viable and easy to implement. Crucially, the same probes can be used for both TBL and WL deployment techniques
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2D Modelling of Satellite Gravity and Magnetic Data Along East-West Traverse Line of Peninsular Malaysia
Authors N. F. D. Bahrudin, H. Umar, W. Y. W. Zuhairi and Y. RahmanSummary2D modelling technique has been carried out based on satellite gravity and magnetic data along east west traverse line across from Kuala Selangor to Kuantan, Peninsular Malaysia with the main aim is to estimate the crustal and mantle subsurface layers. The main focus of this study is to estimate the basement consisting of Paleozoic-Mesozoic sediments, granitoids layer, Bukit Tinggi fault zone, Raub Bentong Suture zone, Lepar fault zone, Conrad and Mohorovicic discontinuities
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Deciphering Land Subsidence in Kediri, East Java through Integrated Geoscience Investigation
Authors P. Sumintadireja, A. Prihadi, A. Saepuloh, F. Perdana, F. Aries, W. Lusano and K. PrabowoSummaryOn April 2017, a natural phenomenon has occurred in a village located in Puncu District, Kediri, East Java. Area in the proximity of several water wells in the village has collapsed. A team of researcher was dispatched in order to investigate what caused the phenomenon and prevent further social unrest. This paper is meant to elaborate the workflow that has been done to investigate the root cause of the land subsidence.
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Tangguh Geotechnics and Geohazards Mitigation Part.1: The big picture
Authors S. A. Putri, C. S. Birt, H. Galanes-Alvarez, T. Manning, R. Apriani, R. Eloni and M. HigsonSummaryThe BP-operated Tangguh LNG project, located in Bintuni Bay, West Papua, Indonesia, is a large, remote multi-TCF gas development. Two LNG trains have been on production since 2009, and the Tangguh Expansion Project will add a third train to exploit gas from smaller surrounding fields, requiring an extensive offshore drilling campaign and related project activities. The shallow overburden is complex, with highly variable soils and a complex distribution of shallow gas. Legacy site-investigation data in Tangguh was acquired in small patches, which are variable in quality, geographically separated and unsuitable for regional geotechnical and geohazard assessments.
To address these issues, a regional shallow survey was acquired in 2016, delivering a high-quality dataset with significant uplift over the small patches of legacy data. Better image quality enables much improved understanding of soil conditions and more reliable correlation of key soil units between geotechnical boreholes for geotechnical engineering studies. High resolution profile images and amplitude fidelity allow more confident shallow gas interpretation and fault mapping for geohazard mitigation. Additionally, the regional shallow survey was acquired under budget and has proven to be very cost effective.
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Tangguh Geotechnics and Geohazards Mitigation Part.2: Solving the puzzle
Authors A. Ramadhan, H. Galanes-Alvarez, S. A. Putri, C. S. Birt and M. HigsonSummaryThis paper has shown that the integration of geophysical and geotechnical datasets by a multidisciplinary team into a ground model can be used to support informed decisions about the development of offshore facilities in Berau-Bintuni Bay. The ground model has evolved with each phase of data acquisition and supported the elimination of initial conservative assumptions as additional data increased the resolution. The ground model enabled the early identification and avoidance where possible of hazardous conditions identified. It also enables, within the limitations of the data resolution, to extrapolate shallow soil conditions beyond locations ‘ground truthed’ with physical sampling. Example applications of this ground model for the Tangguh Expansion Project have been presented informing the selection of acceptable locations for installation and in-place performance of mobile self-elevation jack-up drilling unit foundations within laterally and vertically highly variable sediments affected by active seabed processes. The same ground model has also been successfully interrogated to: decide on the site selection of fixed platforms; support the successful installation of piles and well conductors; refine routing of pipelines to lessen the impact of certain geohazards, such as sandwaves and areas of significant seabed mobility and mitigate the impact of potential seabed liquefaction during seismic events.
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In-situ geophysical and hydrochemical monitoring of landslide dynamics (Pégairolles, Languedoc, France)
Authors P.A. Pezard, S. Gautier, N. Denchik, M. Geeraert and G. HenrySummaryThis paper focuses on the relationship between rainfalls, groundwater flow and in-situ deformation within a landslide body. In relation to more traditional surface measurements, a set of innovative, in-situ and high-frequency monitoring techniques of both hydrochemical and geophysical processes has been deployed in two nearby shallow boreholes. The experimental site is located near Lodève at Pegairolles de l'Escalette, Languedoc (France), an hour west of Montpellier. In this region, the deformation process is linked to intense climatic events such as torrential rains (Cevenol events) and the associated dissolution of evaporites. With a relatively simple geological context and a unique triggering factor, these landslides are natural observatories to study the impact of climatic events on slope processes. Downhole data collected over 5 years from the integrated set of permanent borehole instruments will be presented to illustrate the spatial and temporal dynamics of landslides processes near Lodève, shedding light on the relationships between rainfalls, ground water flow and deformation. The data recorded over time provide constraints to derive physical and numerical models describing the landslide hydrodynamic behavior. Also, the high-frequency monitoring may lead to the identification of geophysical proxys of deformation, which could be used as landslide precursors in the future.
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Tomography of Seismic Wave’s Velocity Structure using Swarm Earthquake Data in Jailolo Area, West Halmahera
Authors B. A. Wibowo, S. Rohadi and SupriyantoSummaryFrom the analysis of seismic recording using JISVIEW, from August 12 to September 12 2016, there are 264 earthquakes detected. After running the simultaneous hypocenter relocation and seismic velocity (P waves) tomography inversion, we found 219 earthquakes that can be relocated and used in seismic tomography inversion. From the seismic velocity structures, 3-D slice from various lines ( Figure 1 ), we found a high contrast of P-waves velocity that concentrated in the middle of Jailolo Bay at the depth from 0–8 km, and spreading to the north and south of Jailolo bay ( Figure 2 ) .This high velocity contrast is interpreted as igneous rock from previous eruption in the past. At 15–30 km depth, the high contrast is replaced by low velocity contrast. The low velocity contrast at the depth between 15–30 km is interpreted as magma bodies that pushing igneous rock above its bodies upward. This magmatic activities are assumed as a source of swarm activites at Jailolo and its surrounding areas in 2015.
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Application of Gravity Method for Local Geological Structures Identification in Surabaya
Authors J.P.G.N. Rochman, D.D. Warnana, A. Widodo, F. Syaifuddin, W. Lestari and A. MahsaSummaryGeodetic study using Global Positioning System (GPS) has been done against the measurement of surface deformation in Java. Fault Kendeng is an active fault that extends from the eastern part of Java East to the western part of Central Java. The Java region obviously had a larger density difference because subduction rate is higher. This study indicated a new major earthquake will threat through East Java and causes tsunami to Bali, Lombok, Nusa Tenggara, and other beaches along the Flores Sea. Geological sheet of Surabaya showed the area of Surabaya and its surrounding are traversed by several structures geology liked the Lidah and Kedung Waru active faults which are associated with Lidah Anticline, Gayungan Anticline and Kedung Waru Anticline. Therefore, Surabaya and its surrounding areas had the potential of an earthquake. The measurement with gravity method can describe the condition of the structure under the surface which includes the interpretation of lithology as well as identify the presence of fault in the city of Surabaya. This study will become additional information for mitigation efforts and reviewing the spatial plan and territory in Surabaya.
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Identification of Groundwater Karst Reservoir With 3D Cave Mapping And 2D Inversi Resistivity
By I TaslimSummaryThis study aims to identify the presence of karst groundwater reservoirs under the surface of the pious cave, Maros, South Sulawesi. This study will integrate with a mapping survey on a pious cave with the inversion of geoelectric measurements. the integration of these two methods can identify the presence of groundwater reservoirs of karst in the area so that it can be managed and utilized in the surrounding community.
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