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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
81 - 100 of 115 results
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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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