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EAGE-GSM 2nd Asia Pacific Meeting on Near Surface Geoscience and Engineering
- Conference date: April 24-25, 2019
- Location: Kuala Lumpur, Malaysia
- Published: 24 April 2019
1 - 50 of 80 results
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Integration of geoelectrical and seismic refraction data by means of fuzzy clustering for landslide investigation
More LessSummarySeismic and geoelectrical methods are powerful tools to investigate the landslides. The effectiveness of the investigation will significantly increase if we can exploit the strength of each method and complement its information into the combination model. The question is how we can put the models together. In this work, we utilize the advancement of fuzzy clustering technique to integrate seismic refraction and geoelectrical datasets in a co-operative inversion process. The fundamental idea to use fuzzy clustering is to build a model that resembles geology, particular rock units. We apply our method to a dataset acquired at Doi Ong Tuong, Hoa Binh province, Vietnam. The dataset includes refraction seismic and direct current data for landslide investigation. Seismic refraction is good at defining a structure to assist geoelectrical inversion. In turn, the geoelectrical method is sensitive to low resistivity media that usually relates to weakened zones, but is not good at structure definition. Our results are consistent with the borehole information. Applying fuzzy clustering again to the models of velocity and resistivity, we can create a clustering map that is more interpretable than using directly the inverted models.
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Characterization of Quaternary Deposit in Seberang Perai Selatan, Pulau Pinang Using Active, Passive and Hybrid MASW
Authors J. Ariffin, M.A. Mohamad Ismail and M.F. MohammadZakiSummarySoft quaternary deposit is widely found in Seberang Prai Selatan, Penang which consist of marine clay, silt and few thin layer of sand. Due to actively development of the rural part, assessment of soil before substructure design is becoming top priority. This study aims to provide a reliable characterization as a guide for marine clay properties estimation using in situ data of one-dimensional shear wave velocity using Active-MASW, Passive-MASW and Hybrid-MASW. The lowest Vs30 observed from Active MASW method (111.59 m/s) while highest Vs30 observed to be from Hybrid MASW (173.60 m/s). In overall, result of Vs30 using Passive MASW is approximately similar to Hybrid MASW. Active MASW-Hybrid MASW relationship show weak correlation with R2=0.12 while for Passive MASW-Hybrid MASW show strong correlation with R2=0.91. Active MASW-Passive MASW are weak correlated with R2=0.106. Combination of these methods which is Hybrid MASW must be referred in order to obtain reliable Vs along subsurface depth.
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Near-surface 2D seismic survey in the transition zone near Sakhalin island: case study
Authors A. Konkov, A. Turchkov, A. Oshkin, V. Ignatev, I. Polikarpov and A. SimakovSummaryThis paper is based on the results of shallow 2D seismic survey performed in the transition zone (land-shallow water) at the construction site of a bridge between mainland and Sakhalin Island (Eastern Russia). The purpose of the research was to obtain geological sections in the transition zone, that are necessary for further linking of marine and land seismic data. A special attention was given to assumptions on location of the upper boundary of a rocky base.
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Estimation of Anisotropy-Free Acoustic Impedance from Partial-Stack Seismic Inversion: A Case Study From Inas Field, Malay Basin
Authors M. Gouda, A.M.A. Salim and G. HamadaSummarySeismic velocity is a pivotal geophysical property that contains important information about Earth layers. The layering of Earth, clay content and fractures within layers are the main causes of the dependence of seismic velocity on the angle of incidence which is called: “Seismic Anisotropy”. Seismic anisotropy affects the velocity-dependant attributes such as Acoustic Impedance resulting in misinterpretation of seismic data. Consequently, anisotropy correction of acoustic impedance is important to mitigate the uncertainty. Anisotropy parameters can be obtained from core data and well logs with various methods. However, the common limitation in the previous work is that anisotropy is obtained at well locations neglecting the lateral heterogeneity of layers. This study aims to obtain anisotropy-free acoustic impedance (Zp0) from the partial-stack inversion of near, mid and far-angle stacks. The outputs of the inversion are used to obtain Zp0 by three different methods: the refactorization of Thomsen’s anisotropy equation, statistical modelling, and the Multi-Layer Feedforward Neural Network Theory (MLFN). The results obtained from the MLFN and the refactorized Thomsen’s model showed better matching with impedance logs, more obvious lateral continuity of layers and more enhanced amplitude spectrum compared to the uncorrected P-impedance. Such improvement reduces the uncertainty of the final reservoir model.
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Elimination of Internal Multiple using Inverse Scattering Series in Malay Basin - A Case Study
Authors H. Hashim, Y.M. Tang, A.H. Abdul Latiff and D.P. GhoshSummaryWith increasing hydrocarbon exploration in deepwater regions, the need to acquire accurate seismic data becomes much more important. One of the main challenges in acquiring seismic data in this area is the presence of internal multiple. This seismic multiples are usually considered as insignificant compared to the surface-related multiples, however if the target areas lies in a deeper region, it becomes much more prominent due to the weaker primary reflections. If this type of seismic noise is not handled correctly, it can effect the seismic reservoir and characterization and thus increasing the risk in oil exploration. Therefore a more advanced method needs to be applied, and one such method is the inverse scattering series. This method is data-driven therefore unlike other internal multiple attenuation technique, its does not require any prior information of the subsurface to predict the multiple. The application of this method in offshore Malay basin shows significant results, as the seismic data produced shows an improvement with a cleaner image compare to the one without any internal multiple removal.
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Reducing ERTM artifact arising from incorrectly imaged mode conversions in the dip-angle domain
More LessSummaryA straightforward and naive implementation of elastic reverse time migration (ERTM) might produce images that are not very useful mainly because they are filled with noises arising from incorrectly imaged mode conversions, cross-talk, and back-scattered energy. Therefore, we present a ERTM workflow that overcomes these problems. We first employ vector-based normalized cross-correlation imaging conditions (VBNICs) for PP and PS reflections to avoid cross-talk and polarity reversal. Based on Poynting-vector imaging condition, we implement angle filtering to reduce low-wavenumber and high-amplitude noise. Then, we efficiently extract dip-angle gathers by using Poynting vectors and finally utilize them to attenuate the artifact caused by non-physical wave-mode conversions because their slopes differ from the migration dip. Numerical examples demonstrate that the proposed ERTM workflow can produce images with less noise and higher quality.
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Site characterization with ambient seismic noise at the Norwegian Geo Test Sites
More LessSummaryThe objective of this study is to find an efficient way to measure bedrock depth and geotechnical parameters through the estimation of shear wave velocity, Vs. The Norwegian Geo Test Sites (NGTS) initiative aims to establish five national test sites as field laboratory for testing innovative soil investigation and foundation methods. We have measured ambient seismic noise data as well as Multichannel Analysis of Surface Waves (MASW) data at two NGTS sites, Onsøy and Halden. The results of the shear-wave inversions are compared with ground-truth measurements from the two well-characterized sites. The results obtained with the passive seismic test and the MASW active test are quite similar despite the fact the passive method requires less time and equipment in the field.
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Soil-Rock Interface Mapping in Jinan urban area using H/V Spectral Ratio of the Microtremor
More LessSummaryThe soil-rock interface is of great significance to urban construction and disaster prevention. In this paper, the H/V spectral ratio (HVSR method) based on the propagation characteristics of microtremor is used to mapping the interface in Jinan urban area, China. The results showed that the H/V curve types are depending on the type of bedrock and its weathering degree. Weak weathered limestone can use this method to obtain a better peak frequency-depth relationship, which can be used to estimate the depth of soil-rock interface in similar areas. However, the intrusive rocks with severe weathering can’t get ideal results.
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Marrying seismic attributes and geomechanical analysis for de-risking induced seismicity in unconventional reservoirs
Authors H. Abul Khair and M. AdamsSummaryInduced seismicity resulted from hydraulic fracturing is an unintended issue, and unpredicted by-product of tight reservoir development. We introduce a new workflow to identify the location and extent of the subtle faults (I.e. below or close to seismic resolution), which may also contribute to the risk of potential induced seismicity. A sequence of post stack seismic processing workflow is introduced. The location of the new identified subtle faults correlates well with the focus of the induced micro-seismicity events. Most Positive Curvature attribute identified a constant NW-SE fault orientation parallel to the Rocky Mountains. The stresses and pore pressures resulted from Mechanical earth models (ID MEM) were then applied on the interpreted faults, and fault susceptibility analysis was conducted. The authors suggest that N-NNE trending faults oriented to current day in-situ stress are critically stressed. This workflow offers a solution to avoid such critically stressed faults that may be prone to slip. It should be noted, that smaller scaled seismicity events, known as micro-seismicity should not be confused with larger events. This is primarily because micro-seismicity, and any seismicity under a Richter scale value of three are not believed to be associated with damage to buildings, or man-made structures.
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Construction of a 3D velocity model for microseismic event location on a monitored rock slope
Authors Z. Zhang, D. Arosio, A. Hojat, M. Taruselli and L. ZanziSummaryWe are planning a tomographic survey to characterize an unstable rock mass that has been monitored with a microseismic sensor network since 2013. An automatic algorithm is used to classify the events filtering noise and interferences. To interpret the events for monitoring the evolution of the fracture system within the rock mass, we are now developing a hypocenter location procedure. The algorithm needs a 3D velocity model. In this work, we discuss the preliminary source tests performed on site to select a portable source suitable for the harsh environment and the size of the monitored area. The small database generated with these tests has been also used to perform a location exercise using a constant velocity. The results are encouraging but it is clear that a 3D velocity model is required to improve the accuracy. Finally, the database has been used to perform a tomographic exercise to extract a preliminary 3D velocity model. The result seems meaningful and shows that despite the difficulties in deploying and moving sources and sensors (a 24-geophone spread will be combined with the microseismic network to increase the ray coverage) in the harsh environment of the rock cliff, the tomographic survey is promising.
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Pseudo-3D dual-frequency induced polarization for dam leakage detection
More LessSummaryThe dual-frequency induced polarization method has been applied in geophysical exploration for many years. Pseudo-3D dual-frequency IP array has also been improved based on the traditional 2D IP data acquisition system. In this study, we employed the method in the dam leakage detection. However, due to the limitation of the topography of the surveying field, 3D array is not the efficient way to acquire the dam leakage data. Based on the 3D resistivity cube, we infer the channel of the leakage in the dam. We give two possibilities of the dam leakage path.
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New wide-band EM system ARMT-5: case study - CSAMT survey at potassium deposit in frequency band 10Hz - 100 kHz
Authors A. Simakov, A. Shlykov and V. IgnatevSummaryThe new wide-band EM system ARMT-5 described in the abstract combines features of AMT and RMT devices. It is designed for implementation of a variety of electric survey methods: AMT, CSAMT, CSEM, RMT and CSRMT. Its wide frequency range (0.1 Hz – 1 MHz) enables the applying of this tool for the exploration of depths from first meters up to several kilometers for a broad spectrum of targets. CSAMT survey with this equipment has been successfully applied at the potassium deposit for recovering the geological structure at the depth of 300 meters. Measurements have been done in frequency band 10 Hz - 100 kHz.
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Analysis of Geophysical Datasets for Coastal Vulnerability and Asset Management
Authors P. Eccleston and A. SpyrouSummaryAnalysis of Geophysical Datasets including seismic refraction, MASW and Ground Penetrating Radar to assist with planning for coastal vulnerability and asset management along the sandy coastline of south west Western Australia
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Delineation of elastic properties and settlement of dam materials at the dam embankment using seismic methods
Authors S. Yordkayhun and K. WattanasenSummarySeismic refraction tomography and MASW analyses provided 2D compressional (Vp) and shearwave (Vs) velocity sections along the crest and downstream side of the Klong Sadao dam. The results of Vp and Vs investigation have shown that the settlement of material of the dam embankment is increasing with depth. Based on Vs30 values, the area falls in site class C and D, indicating the stiff soil to dense soil and soft rock beneath the dam. There are noticeable regions of weak zones as indicated by determined Poisson’s ratio. In addition, the calculated predominant period of the dam suggest that local earthquake with 0.1-0.4 s period can pose significant threat to the dam.
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Effects of irregular topography on Rayleigh-wave propagation in surface-wave exploration
Authors H. Yamanaka, S. Miyanaga and K. ChimotoSummaryWe have conducted finite difference simulation of wave propagation in a 3D shallow soil model with a surface irregularity similar to a river embankment. We found large scattering waves from edges of the surface layer in the synthetic vertical waves at sites on the surface along a surveying line of the crest. The scattering waves do not have significant effects on the dispersive features of Rayleigh waves at the sites close to the source location. However, the effects is large for the sites far from the source, and makes it difficult to apply ID surface wave theory to interpret observed data in the surface-wave exploration.
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Application of Geophysical Investigation to occurrence of settlement - A case study
SummaryOver the past several decades there has been a steady increase in the application of geophysical technique to many type of civil engineering problems. Main applications included the determination of depth of bedrock and physical properties of rock (Sharma 1997). Recently, geophysical method has become the alternative method of soil investigation due to cost, time efficiencies, and the quality of their researches (Sam Setchell, 2016). In this case study, occurrence of crack at house structure due to soil settlement had become one of problematic issues in geotechnical investigation. With the support of geophysical method, the characteristic and soil category can be determined.
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Petrophysical and Geotechnical Evaluation of Mesozoic Rocks from Central Lebanon
Authors M. Salah, M. Alqudah, A. Monzer and C DavidSummaryWe conducted several petrophysical measurements on forty nine core samples collected from the Jurassic and Cretaceous strata exposed at west central Lebanon to evaluate their petrophysical and elastic properties and study the effects of the depositional conditions, sediment composition, and subsequent diagenetic processes on the measured parameters. First, these rocks were petrographically studied to identify the lithofacies, porosity, and the main diagenetic features. In addition, these rocks were investigated under the scanning electron microscope (SEM) and by the X-ray diffraction (XRD) analysis to identify their mineralogy. The petrophysical measurements were performed on the core samples where porosity, permeability, bulk and grain densities were first determined, followed by measuring the seismic wave velocities. The main lithofacies of these rocks can be categorized mainly into carbonates and siliciclastics. The SEM and XRD analyses revealed that the main constituting minerals are calcite, quartz, dolomite, beside other accessory minerals. The studied rocks have generally low to moderate porosity, moderate to high bulk density, and very low permeability. The average Vp and Vs are 4263, and 2323 m/s, respectively, giving a Vp/Vs ratio of 1.83. We further calculated the elastic moduli of the studied rocks and established a number of relationships between the measured petrophysical and acoustic properties to examine their mutual interdependence and evaluate the effects of porosity, rock composition, depositional and diagenetic processes on the measured rock characteristics. We found that some samples, mainly carbonates, deviate significantly from the expected porosity-velocity and density-velocity trends. It is thought that coring-induced microcracking, originally-present micro- and intercrystalline pores in these carbonate rocks may account for these outliers.
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Characterization of the hot spring aquifers at Sungai Klah using potential fields geophysical methods
Authors J.S. Kayode, H. Arifin, M. Nawawi, A. Khalil and H. BaioumySummaryThe potential geophysical methods using gravity and ground magnetic were applied in an integrated strategy to characterized and lessen the ambiguities of the models generated. The gravity method was adopted to define subsurface rock contacts, (i.e., dykes and faults), using their density contrast. The Bouguer gravity anomaly map was generated from the data with the 3-D Euler deconvolution techniques applied in Geosoft Oasis Montaj software to delineate these rock contacts and sources of the subsurface anomalies emplace in the area thereby making it a powerful technique for assessing the depths and the geometry of the buried geologic sources for the hot water reservoir. The total intensity magnetic values recorded were corrected and plotted on a magnetic map for quantitative modeling and interpretation. The Euler deconvolution and Reduced-to-the-Pole (RTP) filters were applied to the data to produced more reliable detailed of the subsurface structures beneath the hot spring. Applications of integrated geophysical tools in addition to a well-known geology of the area under investigation minimizes ambiguities. The models obtained from the geophysical surveys showed that the aquifer could be probably at a few hundred meters deeper than the predicted.
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Heat flow distribution in southwest China calculated from the Curie depth
More LessSummarySouthwest China has well-developed geothermal resources due to the complete and intense geotectonic activities. Heat flow is an important geophysical property to represent thermal state of the earth and it is closely related to the Curie depth. Most previous studies are mainly based on estimation of heat flow from the Curie depth. To improve the quality and accuracy of heat flow, we propose an iteration approach of calculating the heterogeneous thermal conductivity laterally. Firstly, we calculate the distribution of surface heat production using the data of radioactive elements. Secondly, the thermal conductivity is obtained under the constraint of the Curie depth and surface heat production. Finally, the heat flow and its value underground of the study area can be obtained. The results show that the surface heat flow of southwest China is in line with the background trend of high in the southwest and low in the northeast. The surface heat flow are basically corresponding to the measured heat flow and regional geothermal anomaly.
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A preliminary ground magnetic and resistivity investigations on Deidei geothermal area, Papua New Guinea
By P. IrarueSummaryThe linear discontinuity in the magnetic data pattern which separates the contrasting magnetic intensity areas to the north and south coincides with the location and orientation of the major east-west trending and southerly dipping near vertical fault structure observed at Galagalalana and Seuseulina thermal sites in the west and also with the Bolousunamo fumarole site on higher land area toward the east. Moderate to low magnetic intensity anomalies were concentrated toward the south side of the linear discontinuity thus indicating intense hydrothermal activity (or alteration) toward the south. This also suggests that the localized up flow on the structure (faults) may have been pushed toward the south due to the N-S hydrological gradient thus causing demagnetization to the south. A preliminary model proposed for Deidei geothermal system suggests neutral chloride outflow at low land areas (Seuseulina and Yaiyaiboalana boiling springs) towards the west and steam and hot pressurized water up flow at higher land areas (Bolousunamo acid sulphate fumarole) toward the east.
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Multi-channel GPR surveys for the detection of archaeological remains: A case study from Öland, Sweden
Authors A. Viberg, J. Adcock and M. LangtonSummaryMulti-channel GPR surveys have quickly become a popular method for archaeological prospection worldwide. The instruments often produce high-resolution data, and as the multi-channel arrays are often motorized, the instruments can collect data over large areas fast. In Scandinavia, and in many areas in northern Europe, where the archaeological remains often are very small, the introduction of multi-channel GPR has vastly increased the possibilities of successfully mapping and correctly interpreting these elusive features. This article aims at demonstrating some of the benefits of using such a GPR system for archaeological surveying. A case study from the Island of Öland, Sweden is presented where the Mala Imaging Radar Array (MIRA), 16 channels, 400MHz, was used for mapping the buried archaeological remains inside a large ring fort. The interior of the fort is roughly lha in size and the survey took approximately 3 hours to complete. The results clearly reveal both Iron Age and Medieval building remains within the fort’s perimeter wall as well as internal house structures such as hearths and post holes. This highlights the benefits of using similar systems for archaeological surveys elsewhere.
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GPR method as an efficient NDT tool to characterize carbonate rocks during different production stages
Authors A. Hojat, M. Izadi-Yazdanabadi, S. Karimi-Nasab, D. Arosio and L. ZanziSummaryIran and Italy have a great potential in stone production relying on a variety of dimension stone quarries, especially carbonate rocks. To survive in the modern challenging international market, it is crucial to have products without defects. Ground Penetrating Radar (GPR) method as a rapid and efficient non-destructive technique (NDT) can be used to characterize carbonate rocks during different production stages. In this paper, we present the results of GPR measurements to monitor the quality of marble and limestone rocks at different scales. Considering the availability of GPR antennas in a wide range of frequencies, providing different resolutions, GPR method is very encouraging to detect the desired discontinuities of carbonate rocks at different production stages. Lower frequency antennas can detect major discontinuities to optimize the extraction design. Higher frequency antennas can later detect smaller fractures of the extracted blocks to optimize slab production. Our research is under progress to explore the efficiency of GPR method in mapping the quality of resin injection in fractured rocks. As an auxiliary NDT method to be integrated with GPR measurements, ultrasonic pulse velocity tests are also performed. The results show that changes in the velocity can be a good indication of the stone quality.
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Analysis of post-landslide electric imaging data at a site in Sapa, Vietnam
More LessSummarySapa town is located on a mountainous area of Lao Cai province in the north of Vietnam. It is one of the most attractive tourist places of the country. The recent and frequent landslides and displacements of the only hillside road connecting Sapa with other parts of Lao Cai have caused public concerns and required the site investigation to find out measures of mitigation and control of this geohazard. Boreholes were drilled, samples were taken and laboratory geotechnical testing were conducted. In addition, 6 lines of electric imaging (EI) that includes three line parallel to the slope direction and three other cross lines were conducted using a dipole-dipole array by means of the SuperSting R8 resistivimeter. The first results of this this research is to come up successfully with a data processing procedure to correct the irregular positions of the electrodes placed on a rugged terrain surface of a mountainous slope to make the EI data ready to be properly inverted either by EarthImager2D or RES2DINV software. The EI data along a survey line (Line 2) were selected for analysis, whose results could be integrated well with the laboratory measurements of resistivity and geotechnical investigation data to define well the weathering profile of the rocks at the study site that can be used in a slope stability analysis to further find out the most probable mode of landslide in the study area
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Landslide Assessments Using Integrated Geophysical Methods; Granitic Area of Hulu Yam
Authors M.T. Zakaria, N. Mohd Muztaza and A.T. OlugbengaSummaryInstability of natural slopes is geomorphological event that effects changing of the Earth’s surface and known as a universal natural hazard which has always brought to significant economic losses, human lives, infrastructures and other facilities. Hence, developing a scientific comprehension of geological and physical process of earth’s rheology are important to evaluate and to conduct a predictive model for hazard problems. Therefore, 2D resistivity and seismic surveys were used to visualize the failure zones of the landslides. The six 2D resistivity survey lines and three seismic refraction lines was conducted in Hulu Yam area as study cases for landslide area. The correlation of 2D resistivity and seismic refraction result show the Hulu Yam area consists of two main zones which are highly weathered zones and granitic bedrock. The sliding zones identified at the layer of highly weathered zones at resistivity values of 1200-3500 Ωm. A bedrock was identified at depth >40 m with resistivity and velocity values of >7000 Ωm and 3700-5600 m/s respectively. The volume of mass sliding is estimated based on the integrated result of 2D resistivity and seismic refraction of all survey line using Trapezoidal rule calculation
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Engineering geological investigations of landslides in Auckland, New Zealand
By M. BrookSummaryThe undulating topography of the Auckland urban region of New Zealand is susceptible to landslides of varying process-mechanisms, including: (1) earthflows of saturated Pleistocene Tauranga Group sediments, tephra and residual soils flowing off more competent underlying rock; (2) rotational slumping of man-made fill or Tauranga Group sediments; (3) block-slides of weak Miocene Waitemata Group sedimentary rock, dipping out of slope. Such landslides are often triggered by intense short periods, or prolonged periods of rainfall, such as the ‘Tasman Tempest’ and ex-Tropical Cyclone Debbie storms of 2017. Typically, rainfall infiltration results in a rise of the groundwater table and an increase of the pore water pressure, causing a reduction in effective normal stress and thereby soil strength, leading to landslides. Here, some case studies are presented of landslide investigations in Auckland using geophysics such as ERT and EM to monitor subsurface hydrogeology, in conjunction with Unmanned Aerial Vehicles (UAV) to monitor topographic change.
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Characteristics of Muria Vulkanism and Tectonic Impact at Development of Nuclear Reactor in Muria, Central Java
Authors V.C. Latengke, I. Faiqi, P.A.S.M. Dewi and E.N. NainggolanSummaryIndonesia is included in the country with the presence of thorium as nuclear fuel. Proposing the construction of a nuclear reactor in the Muria peninsula area has long been proposed but until now development has not yet been carried out. This research provides the latest recommendations regarding the history of eruptions, the characteristics of magma and the effects of volcanism and tectonics found in Muria Volcano located in the northwest of the nuclear reactor construction area by using library study methods, morphological analysis, field observation, petrographic analysis and geochemical studies. Young Muria vulkanism was produced in 320 thousand years ago with no detectable volcanic activity since human life with maar Bambang presence that older than young Muria volcano. The characteristics of magma were ultrapotasic series magmas in the middle-base lava series and the calc-alkaline potassic group or in the shoshonitic series which come from cooling magma that contact with ground water so that it usually produces phreatic eruptions but does not produce magmatic eruptions in the near future. Indications of faults in the Muria Volcano which is predominantly northeast directed by active tectonics because it is young so that tectonic earthquake hazards are most likely to occur
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2-D Electrical Resistivity Tomograph & Induced Polarisation Survey on Detection of Karst Features
Authors C.N. Tiong, S.S. Liew, F.W. Chee and H.Y. YongSummaryThe presence of naturally formed voids/cavities and solutioning channels in the subsurface karstic limestones can cause severe problems in civil/geotechnical engineering and mining projects. Peninsular Malaysia has various types of karstic limestone, sinkholes, solutioning cavities and channels. To effectively appraise the karstic formation, electrical resistivity and induced polarisation techniques have been proven a cost-effective solution for investigating subsurface bedrock profile, solution channels and its connectivity. A case study using 2-D electrical resistivity tomography and induced polarisation survey for a limestone quarry site is used to illustrate the successful application in identify the location of the karst features. Data processing has been carried out taking into consideration of the collective response of resistivity and induced polarization (IP)/chargeability that helps in interpreting subsurface strata, seepage path in the upper alluvial deposits, location of porous/jointed limestone rock mass or/and karst features with potential seepage flow, and the infilling condition of the joints and voids.
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2D ERT for the investigation of the subsurface structures at the Egiin gol site, Northern Mongolia
Authors K. Tseedulam, S. Khishigsuren and Y. BolormaaSummaryTwo dimensional Electrical Resistivity Tomography methods was used to investigate a proposed dam site in Egiin gol, northern Mongolia, to delineate the nature of the subsurface structures to assess its suitability for the construction of dam. The main objectives are to investigate the depth to the bedrock, possible geologic structures, such as possible presence of faults, fractures, voids and clay in the dam axis and abutments. The selected method has the possibility to give an image of the subsurface and map lateral and vertical variations in the subsurface geology of the site. Total 7 2D electrical resistivity tomography profiles with Wenner-Schlumberger array were conducted, the space between electrodes is 5m and the lengths of the profiles are 240 m. The depth of the investigation is assumed to be 40 m. These results are confirmed and verified by using several boreholes data were drilled on the recommendation of the surveys. The results showed that the Egiin gol site is suitable for the construction of the proposed dam
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The inversion of 2-D and 3-D resistivity data from surveys in aquatic areas
More LessSummaryResistivity surveys are now also carried in areas covered by water. The surveys involve electrodes planted on the water bottom or on a streamer towed by a boat. As the water layer has a large effect on resistivity measurements, its effect must be accurately modelled. The water resistivity and depth to the bottom are usually independently measured with a conductivity meter and depth sounder. The upper part of a finite-element grid is used to model the water layer, including possible variations in the water resistivity with depth. We show the results from a 2-D survey in Stockholm with electrodes planted on the sea bottom. The sediment thickness from the inverse model agrees well with drilling results and a possible weak zone in the bedrock was detected. Surveys with floating electrodes do not follow a straight line due to water currents and a 3-D inversion approach is required. An example is shown from a survey in the Panama Canal where the data from 19 sub-parallel lines are collated into a 3-D data set. The inverse model shows a conductive bottom with weathered marine sedimentary rocks and a remnant of an old river channel filled with more resistive sands and gravels.
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Soil Properties and Behaviour Studies using Joint-interpretation of 4-D Electrical Resistivity Tomography and Soil Mechanics Methods in Penang, Malaysia
Authors A.A. Bery, N.E.H. Ismail and N.M. MuztazaSummaryThe paper presents the integration of geophysics and soil mechanics methods in investigate the properties and behaviour of clayey sand soil properties for slope study from March until April. The geophysical method used in this study is 4-D electrical resistivity tomography (ERT), meanwhile soil mechanics used several laboratory tests, namely direct shear, moisture content, porosity, plastic limit and liquid limit. The infield survey using 4-D ERT was conducted for three different months and soil samples were collected along the survey line. The model resistivity with topography obtained showed all the ERT results gave a good results with RMS error between 2.4 - 2.4 %. Based on the model resistivity results, the subsurface of slope area can be divided into two main zone, dry clayey sand soil (100 - 550 ohm.m) and clayey sand soil (550 - 1300 ohm.m). The model resistivity results showed there are changes in electrical properties of soil, which associated with the moisture content, porosity and structure of soil itself during the three months of investigation period. In conclusion, the integration of both ERT and soil mechanics methods are capable to investigate the clayey sand soil’s properties and its behaviour during three months period.
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DInSAR-based estimation of subsidence rate along an UMRT line in Hanoi
More LessSummaryConstruction of the Urban Mass Rapid Transit (UMRT) lines in Hanoi have been considered since the 90s of the last century, and it starts to be conducted now to meet the increasing transport demands of the people living in this capital city of Vietnam. There is a concern that whether or not land subsidence due to groundwater extraction would affect the UMRT lines. Besides the conventional monitoring of subsidence, newer methods using satellite images such as DInSAR should be considered and applied. One of the limitations of DInSAR application is effect of decorrelation noises on quality of Interferograms. In this paper, the factors that may affect the DInSAR results were discussed, including general decorrelation noise and the selection of reference point. A case study for Hanoi city was conducted by two methods; DInSAR and one-dimensional finite element (FEM) consolidation analysis, to estimate the subsidence rate along the UMRT line No. 2. The results of this study showed a good match and consistency in the results obtained by these two methods. Consequently DInSAR is recommended for further land subsidence analysis for other targets in the urban area of Hanoi.
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Quantification of weathering profile based on durability for heterogeneous siliclastic Sedimentary rock in Malaysia
Authors A. Anuar, H. Mohamad and A.G. Md RafekSummaryThe objective of this work was to quantify weathering profile based on durability for heterogeneous siliclastic sedimentary rock. The current engineering geological weathering classification is qualitative which is less suitable for engineering purposes especially for heterogeneous sedimentary rock. In current work, modified-wetting-drying test were performed because no sample preparation is required. Recemented sandstone did not react or change when subjected to 3 cycles of modified-wetting-drying testing. Unlike the moderately to highly weathered shale, rock samples disintegrated from each cycle. The disintegrated samples from each cycle were sieved to determine the fragment size distribution. Different weathering grades showed different patterns of fragment size distribution for slightly weathered recemented sandstone, moderately weathered and highly weathered shale.
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Preliminary Feasibility Study Based on Resistivity Volumetric Calculation : Andesite Quarry
Authors A. Aries Furkhan, A. Adipta, W. Seno Giamboro and Y. YatiniSummaryThis paper will discuss the preliminary examination of andesite quarry mining feasibility in due respect of the volumetric reserves and its overburden thickness. The volumetric reserves were done by calculating the andesite tonnage that utilizes the volume-based resistivity characteristics and density. In addition, overburden thickness was estimated between the top andesite and the topography elevation. The study concluded that the amount of andesite reserves are viable enough to be further detailed mining study.
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Magnetotelluric (MT) Data Analysis and 2D Modeling of the Kutai Basin, Indonesia: Preliminary Results
Authors S.M. Irawati, Hidayat and H. GrandisSummaryMagnetotellurics (MT) is a passive electromagnetic method that measures fluctuations of electric and magnetic fields at the earth’s surface. In this study, MT method is applied for basin delineation based on the resistivity contrast between sediments and basement. Thirty MT stations were deployed at eastern part of the Kutai basin, East Kalimantan, Indonesia. We analyzed the MT data using phase tensor analysis, to obtain the dimensionality and the geoelectrical strike of the subsurface. Most of the MT data are characterized by phase ellipse and low skew value (-3o < β < 3o). This indicates that MT data have 2D character with the direction of geoelectrical strike N 30o E. This result is in a good agreement with the geological strike that of NE-SW direction. We performed 2D modeling at two lines to obtain the resistivity configuration of the Kutai basin. The low resistivity anomalies may be associated with shale or black shale of the Pamaluan Formation showing geometries influenced by Samarinda anticlinorium and its fault structures.
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Sedimentology of Semanggol Formation at Pokok Sena, Kedah
More LessSummaryThrough time, the excavation and earth quarries activities have been increased rapidly and this process also occurred at Pokok Sena, Kedah. Due to this activites, the study on the sedimentary depositional processes which related with Mahang Formation, Kubang Pasu Formation and Semanggol Formation is achievable. The research is intended to discover the boundary that have been separated the three formations. The localities visited for this research are Kg. Kebun 500, Kg. Jabi, Wood Factory area, Kg. Rambutan, Bukit Barak Quarry and Bukit Tembaga. The localities are believed to be part of chert unit and might be part of rhythmite unit. Through the visitation, the main lithofacies found are bedded chert, black mudstone, interbedded sandstone and shale, siliceous shale, interbedded chert and shale and massive sandstone. There are some turbidite deposits such as load casts and mud clasts. Observing the distribution of the lithology deposited within the research study area, it can be suggested that the depositional setting is deep marine environment. The presence of turbidite deposits might due to the turbidity currents that existed during the deposition of the rhythmite unit. This comes to the preliminary conclusion that the research study area is near to the rhythmite unit area. However, more study need to be done to define the depositional process accurately. The preliminary results are recorded using the sedimentary loggings.
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The application of MT method for overthrust geological structure
More LessSummaryThe case in this article illustrates that MT based on the resistivity contrast between strata provides a very important clue for seismic to study overthrust nappes and deep seated structures
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The pre-salt regional structural framework of Kwanza and Lower Congo basin, offshore in West Africa revealed by gravity and seismic data
More LessSummaryThe Kwanza and Lower Congo basin region belongs the to the South Atlantic passive continental margin, which recently became of interest for global oil and gas exploration. In order to clarify the pre-salt structure and further guide exploration in this deep water area, targeted data processing and comprehensive analysis have been done for satellite gravity. In combination with the interpretation of seismic profiles at key structural sites, the overall uplift, burial pattern and the distribution of fault system are summarized. This can provide the reference for the delineation of favorable exploration zones.
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Under Gas Clouds Effects Shallow Marine Gas Reservoir Delineation
Authors E.W. Purnomo, A. Biswas, D.P. Ghosh and C.W. SumSummaryNew approach in seismic attribute and elastic impedance inversion has been used for identification of shallow gas clouds and characterization of deeper gas reservoir of under effected gas clouds shallow marine gas field, Malaysia. The novelty of the method, notably, it used Quality Factor Q and other thin-bed sensitive seismic attribute to constrain stochastic elastic impedance inversion. With the help of ANN and PCA, the inversion defined the relationship between input (seismic or Q, and other constraints) with the well log data. As the Q represented the porefluid characters, the method enable the direct definition of relationship between the earth elastic properties with Q data such that the estimation of elastic properties can be taken from Q data.
Combination of inverted Vp/Vs, Variance and P-wave Quality Factor, Qp, is able to map the shallow gas clouds such that it can help the identifying potential drilling (shallow gas) hazard and study of petrophysical system in the area. The elastic inversion showed that the proposed inversion was able to delineate the considered thin gas sand reservoir from the field, conformable with log and seismic data, and significantly enhanced sand continuity beneath gas clouds.
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Utilization of Air Wave to Determine the Quality of Seismic Refraction Data in Near Surface Geophysical Survey
Authors E. M. H. Masyhur, A. G. M. Rafek and K. A. M. NohSummaryThis study has highlighted the reliability of air wave as a reference to determine the quality of seismic data especially for seismic refraction in near surface exploration. The velocities of the air waves recorded in the seismograph are 364 m/s and 370 m/s. These air wave velocities are within the range of speed of sounds in the air. The seismic data are in acceptance quality.
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Seismic Hazard Zonation using Probabilistic Method in Sukabumi, Indonesia
Authors N. Latuconsina, B. Sunardi and S. SulastriSummarySukabumi is one of the areas in Indonesia which have high seismic activity because it is located near Collision between Indo-Australian Plate and Eurasian Plate. Seismic activity in Sukabumi is not only caused by subduction zones (benioff and megathrust), but also caused by faults, both local and regional. Study about seismic hazard in Sukabumi is done by calculating earthquake ground motion using probabilistic method. The ground motion is calculated using attenuation function that describes the correlation between the local ground movement intensity, the earthquake magnitude and the distance from the earthquake’s epicentre.The results of this research is seismic hazard zonation for 2% probability to be exceeded in 50 years based on earthquake ground motion estimation in PGA (Peak ground acceleration) value, response spectral acceleration in low period (T= 0.2 s), and response spectral acceleration in high period (T = 1.0 s). The acceleration’s range results is 0.533 gals - 0.73 gals for PGA, 0.834 gals - 1.297 gals for response spectra in low period, and 0.22 gals - 0.34 gals for response spectra in high period. Based on the analysis, the areas with the highest hazard levels are Cikembar, Nyalindung and North Jampang correlate with presence of faults.
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Characterization of Dolostone and Limestone in Perlis by Using X-Ray Powder
Authors F.H.A. Fadzil, N.M. Mustaza and Y.J. TeohSummaryCarbonate rock are sedimentary rock that contained carbonate mineral such as calcite, dolomite and aragonite. Limestone (calcite) and dolostone (dolomite) are two main carbonate rocks. Perlis is made up of continuous succession of Paleozoic rock, which are Machinchang Formation, Kubang Pasu Formation, Setul Group, Chuping Formation and Quaternary alluvium (Jones, 1983). Carbonate rocks are found in Setul Group and Chuping Formation. In Perlis, new location of these carbonate rock formations was discovered (Lee, 2001; Harun and Jasin, 2000). In this study, geochemistry method (XRD) is used to characterize carbonate rock at the new site. The findings show that Setul Group’s carbonate rock consist of ankerite while Chuping Formation’s carbonate rock consist of calcite and dolomite with high quartz content. Presence of ankerite depicts the rock underwent a very high temperature during its lifespan.
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Magnetic source depth delineation of the Mulgathing Trough beneath cover in the Gawler Craton, South Australia
Authors C. Foss, T. Wilson, G. Gouthas, L. Katona and P. HeathSummaryA new regional aeromagnetic survey over the Gawler Craton of South Australia has provided new constraints on the extent, structure and depth of the Mulgathing Trough, a Permian age extensional basin developed over a strongly magnetised Proterozoic basement and completely concealed beneath younger cover. We present a study using sweet-spot depth analysis to map depth to basement beneath the trough.
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Aeromagnetic anomaly mapping of possible heavy mineral accumulations in the Coompana area of South Australia
More LessSummaryAn aeromagnetic survey over the Coompana area of South Australia has revealed magnetic anomalies distributed across the area due to near-surface magnetizations. Surface rocks are limestones and calcretes in an arid plain. A possible source of the anomalies is magnetite in heavy mineral concentrates introduced in a previous cover material that is now removed.
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A wavenumber-domain iterative approach for magnetic 3-D imaging with depth constraints
More LessSummary3-D imaging is a significant approach for qualitative and quantitative interpretation of magnetic data. In this paper, a wavenumber-domain iterative approach for 3-D imaging is proposed, which can improve the imaging efficiency and is suitable for rapid imaging of large-scale magnetic data. The wavenumber-domain forward and imaging equations of total magnetic anomaly, magnetic three components, magnetic gradients and magnetic full-tensor gradients are derived. Then, depth-scale factor and magnetic interface constraint algorithm are involved into the imaging processing, which dramatically improve the depth resolution. In order to reduce the deviation and improve the imaging accuracy, an iterative algorithm is utilized. The validity and feasibility of this approach can be verified by the synthetic data.
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State of the arts and new advanced ERT instrumentation and methods for Urban planning challenges
Authors C. Truffert, J. Gance and O. LeiteSummaryMany countries will face challenges in meeting the needs of their fast growing urban populations, including housing, water resource, transportation facilities, energy supply, and other essential infrastructures. Geotechnics has been on a dominant position in the tool box of urban planners. Nevertheless, challenges are getting more crucial since megacities grows so fast and human health being becomes more and more a non-negotiable objective. Underground comprehensive geological knowledge is then the key issue for a safe urban planning. Among the geophysical tools box, urban planner and decision makers have ERT state of the art and advanced development for accessing to a comprehensive underground geological knowledge.
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Developing Geological Model From Electrical Resistivity (ERT) Survey Data for Construction Purposes: Case Studies
Authors F. Dali, A.R. Jaapar, A.F. Abdul Rahim, M.F.S. Md Aripin and Z. MohamadSummaryElectrical resistivity survey is a geophysical method widely used in construction industries to investigate the subsurface geological profile anomalies of the section. Subsurface profile is depicted by pseudo section model that shows difference range of resistivity value. This indicates the different layer of soils, presence of groundwater, boulders or fractured bedrocks zones. The complexity of geomaterial subsurface cause the interpretation of geophysical data become tedious and sometimes inaccurate especially for tropical region like Malaysia as the physical and chemical weathering are very rapid. These weathering change the parent behaviour of bedrock and makes underground very complicated. Ten (10) resistivity set up established at two (2) different sites in Selangor/Kuala Lumpur. The problem encountered by geotechnical engineer during the early phase of the ground investigation was the existences of boulders/rocks fragments in the subsurface that give will affect the construction foundation (Site A); and potential geohazards along the slope section near to the residential areas (Site B). Apart from resistivity survey, boreholes information that was conducted by drilling contractor also optimized to interpret and develop the geological model for the study areas. A very good geological interpretation really appreciated by geotechnical engineers/decision makers to solve construction issues regarding the geological materials at site.
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Distinction of the Type of Mudstone at Bukt Chondong, Perlis Using 2-D Resistivity Method
Authors N. Mohd Muztaza, N. Ahmad Nawawi, M.T. Zakaria and T.O. AdeekoSummaryThe study explores the use of 2-D resistivity method to identify the type of mudstone from the outcrop of Bukit Chondong (BC), Perlis. The distinction of mudstone is based from the comparison of resistivity values of different mudstone, which are the red mudstone and the grey mudstone from outcrop of Guar Jentik (GJ) and Utan Aji (UA) in Perlis. All the survey outcrops was identified within the same classification of Kubang Pasu Formation. The resistivity survey was performed using SAS4000 Terrameter with Pole-dipole array configuration. The resistivity was implemented on a single 40 m survey line with minimum 1 m electrode spacing. The resistivity data was processed by utilizing RES2DINV and Surfer 10 software which the inversion results was displayed in a form of contouring values. The range of resistivity value for red mudstone is 10 to 150 Ωm and grey mudstone is 120 to 500 Ωm. The resistivity value for mudstone of BC is 20 to 130 Ωm, which fall in the range values of red mudstone. Thus, mudstone of BC has the possible to be classified as red mudstone.
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An Accuracy Test of “Schlumberger” Vertical Electrical Sounding Method in a Sandbox Modelling
Authors I. Arifianto, R.C. Wibowo and M.R.F. PrianaSummaryIn groundwater exploration, a geophysical method is needed to provide information and an overview of the subsurface conditions of the study area, and the most common practice for giving subsurface information is a geoelectric method or resistivity method. During the acquisition of groundwater exploration, Schlumberger Vertical Electrical Sounding (VES) is the most preferred due to convenience and effectiveness. Schlumberger configuration will produce a subsurface profile vertically at an observation point and is the initial step to estimate the presence of aquifers in the groundwater exploration area. However, this method has several geological considerations leading to the inaccurate subsurface interpretation that the presence of dipping layers and subsurface structures such as fault are the main factors. Thus, the presence of that features can affect the modeling of resistivity values and subsurface thickness during interpretation process of the resistivity method. This then becomes the basis of the authors conducting a study that aims to determine the accuracy of the layer thickness produced by the VES resistivity method. However, the existence of subsurface structures is also difficult to predict if there are no supporting by surface data, hence the study modeling of subsurface conditions using a sandbox model will be carried out.
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Installation and validation of a customized resistivity system for permanent monitoring of a river embankment
Authors A. Hojat, D. Arosio, L. Longoni, M. Papini, G. Tresoldi and L. ZanziSummaryDevelopment of early warning alarm systems for hydrogeological risk assessment is seriously under research in different European countries. In this paper, we discuss the installation and validation of a prototype electrical resistivity tomography (ERT) system for permanent monitoring of river levees. ERT measurements were performed on various candidate sections of river embankments in Lombardy and Emilia-Romagna regions in Italy for preliminary evaluation of critical sites to be monitored. Based on careful analysis of all datasets, a critical part along an earthen embankment of the Parma river in Colorno was selected to be permanently monitored. A customized ERT monitoring system using the Wenner array with 48 stainless steel plate electrodes was installed in November 2018. The system is making two measurements every day, sending the datasets to a Cloud platform through the mobile-phone network. Time-lapse analysis of datasets measured by the prototype and control measurements with commercial equipment show that the installed system is operating well. The research is in progress to define the thresholds of instability based on water saturation maps calculated from resistivity sections.
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