6th Asia Pacific Meeting on Near Surface Geoscience and Engineering
- Conference date: May 13-15, 2024
- Location: Tsukuba, Japan
- Published: 13 May 2024
1 - 20 of 136 results
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Subsurface Evaluation with Multiple Resistivity Sounding and 2D Numerical Modelling: a Case Study of Neri Bridge, Southern Ethiopia
More LessAuthors Y.G. Doyoro, C. Lin, B.W. Ermacho, E. Pan and S.K. GelenaSummaryElectrical resistivity imaging is widely used in engineering, but in situations where 2D resistivity surveys are limited, the Vertical Electrical Sounding (VES) method is valuable. This study focuses on evaluating the foundation condition of a bridge over the Neri River in Jinka town, Southern Ethiopia. To achieve this, eight VES surveys were conducted along two parallel profiles. The 2D resistivity modelling was also performed to enhance the comprehension of the foundation depth structure. The VES results were used to create a 2D forward resistivity model, which was then inverted to obtain the 2D resistivity section of the study site. These findings were then compared to core drilling data collected from a depth of 30 m at the bridge pier and on both river banks. The 2D resistivity model effectively distinguishes the overburden materials from the underlying regolith or dense sand. By analyzing the resistivity models and borehole logs, a geological section was constructed, revealing distinct layers, including alluvial deposits, regolith, moderately weathered granite, and moderately to slightly weathered granite. This research not only identifies potential foundation depths and overburden material thicknesses for the proposed bridge but also underlines the need for 2D resistivity modelling in improving 1D resistivity surveys.
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Enhancing Fold Coverage Representation Across Horizons Using Optimized Illumination Mapping in Undershooting Seismic Data Acquisition
More LessAuthors R.W. Nurcahyo, H. Asy’ari and D.E. PuteraSummaryIn seismic modeling, an illumination map visually represents the distribution and strength of seismic waves in a subsurface region. This vital tool aids geophysicists and seismic interpreters in assessing the effectiveness of illuminating a specific subsurface target. Challenges in seismic acquisition design, such as obstacles rendering areas inaccessible, necessitate adjustments to the shot point. A case study illustrates the use of the undershooting method to overcome silting obstacles in the transition zone seismic survey. This involved relocating the source line 1.1 km from the receiver line, effectively navigating around impediments.
Following the source line adjustment, simulations are crucial to gauge the impact on data fold coverage at each horizon. The Illumination Map becomes instrumental in precisely depicting fold coverage for each horizon within the undershooting method. This visualization offers valuable insights into acquisition efficiency, ensuring comprehensive coverage and overcoming obstacles, exemplifying the significance of the undershooting method in seismic exploration.
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Application of Electromagnetic Exploration Using an Uncrewed Ground Vehicle Survey to a River Embankment
More LessAuthors R. Umezawa, M. Jinguuji and T. YokotaSummaryFor an investigation of a river embankment, it is important to identify its weakest areas. Geophysical exploration is an effective method to investigate the soil composition of the embankment and foundation continuously. However, river embankments are long structures, more efficient survey methods are required. In this study, the uncrewed ground vehicle electromagnetic (UGV-EM) method was applied to a river embankment to verify the effectiveness as an efficient survey method over a long distance. Real-time kinematic global navigation satellite system (RTK-GNSS) ensures accurate positional information during continuous measurements. The study conducted surveys along a 2 km river embankment, revealing characteristic resistivity structure below the survey line. The survey speed was approximately 1 km/h, which was efficient enough to survey the long distance.
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Discrepancies in Acoustic Underwater Positioning Information and Topographic Correlations because of Bubbles in the Water Column
More LessAuthors M. Asada, M. Satoh, M. Tanahashi, R. Kubota, J. Sakamoto and S. GotoSummaryThe position of an underwater target, as determined by the acoustic positioning system and topographic correlation, shows a discrepancy because of bubbles in the water column. Topographic data were obtained from an autonomous underwater vehicle (AUV) in the shallow methane hydrate–bearing area off Joetsu, Japan. Discrepancy between the two locations increased when bubbles existed between the AUV and the mothership. The positioning error trend reflected the positional relationship between the AUV and the ship that varied east–west with time, suggesting that bubbles play a role in reducing the velocity of acoustic signals in the water mass. A locational relationship that does not interpose bubbles between the underwater target and the mothership is required to obtain reliable positioning information for acoustic measurement.
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Multiphysical Imaging of Offshore Shallow to Deep Strata
More LessAuthors D. Helland-HansenSummaryA survey over the mid-Atlantic ridge has been acquired with a range of multi-physical data which successfully demonstrates the potential for cost-effective multi-physical surveys by mobilizing all equipment on one vessel. The integrated interpretation shows the complimentary value in several independent sub-surface measurements. Learnings have been made on how to best acquire these data going forward.
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Slope Stability Study Using Ambient Noise Tomography Method in Terengganu, Malaysia
More LessAuthors Y.S. Seik and W.M.J. ChuaSummaryOver the past decades, it can be observed that number of slope failures occurred has been increased across the global. Countries with tropical climate like Malaysia has more prone to the natural disaster due to its humid environment across the year. It is relatively important to have proper mitigation measures to prevent this geological hazard. A preliminary study at several slopes in Terengganu has been carried out, in order to delineate the soil profile and identify the potential weak zones in the investigation area. Passive surface wave method, so called ambient noise tomography, was used in this paper to meet the technical direction of the study. Five linear survey arrays deployed with geophone-interval of 3m was carried out. Several critical weak zones with S-wave velocity lower than 200m/s were identified across the survey arrays, especially at higher degree of slope angle. The S-wave velocity profiles are consistent with geological layers in all survey arrays, where greater thickness of regolith overlain the fresh rock. This paper summarizes, the site of investigation, data acquisition, processing and investigation results.
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Imaging Seasonal Moisture Dynamics within a Levee: Two Years of Automated Resistivity Monitoring
More LessAuthors A. White, A. Watlet, J. Boyd, J. Chambers, J. Smethurst, R. Stirling, A. Blake, P. Wilkinson, H. Harrison and P. MeldrumSummaryLevees (flood defences or dykes) play a crucial role in mitigating flood risks, and their long-term performance is linked to their surrounding environmental conditions and internal moisture dynamics. This study presents the results of a two-year automated resistivity monitoring program on a levee in Warden, Northumberland, England. The objective is to understand the seasonal moisture variations within the levee, with implications for its hydraulic conductivity, failure mechanisms and longer-term deterioration. The levee, constructed in 2007, was instrumented with a PRIME resistivity monitoring system, geotechnical sensors, and a weather station. The resulting 2D time-lapse resistivity model reveals three distinct regions: levee core, topsoil cover, and foundation strata, each exhibiting unique seasonal dynamics. The coefficient of variation analysis of the 2D resistivity data over the monitoring period identifies spatial patterns broadly correlating with the known material types. The near-surface zone shows particularly large seasonal moisture content cycles that may drive long-term deterioration. Temporal variability in the levee foundation caused by a fluctuating water table highlights the elevated hydraulic conductivity and the risk of seepage and piping through the foundation strata. This research contributes to our understanding of current seasonal dynamics to better determine the impacts of future climate change on levee performance.
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Rejuvenating Legacy Seismic Data as a Cost-Effective Solution for Subsurface Characterization Aimed at Renewable Energy Installations
More LessAuthors D. Boiero, M. Clementi, F. Ibrahim, N. Seymour and M. BranstonSummaryAddressing climate change and achieving sustainable energy solutions demands a significant scale-up in renewable energy installations, such as large wind farms consisting of multiple wind turbines, while minimizing their environmental impact. However, constructing wind farms requires substantial resources, leading to significant costs, particularly for foundations. Optimizing resource use and cost management becomes crucial to ensure environmentally responsible practices.
To promote effective wind energy projects, geophysical solutions are being explored. Understanding near-surface and near-seafloor characteristics (in marine environments) aids in identifying optimal turbine locations, considering factors like geology and sediment composition. Established geophysical methods, such as surface/guided wave analysis and inversion, provide valuable insights into near-surface and near-seabed (an)elastic properties. These parameters are vital for assessing foundation performance and predicting soil behavior under dynamic conditions, ensuring the safety and efficiency of wind turbines installations.
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Geohazard Risk Evaluation and Mapping Using 3D High-Resolution Seismic Data in Shallow Waters
More LessAuthors S. Kawasaki, A. Hara, T. Kozawa, H. Tanaka and S. LeeSummaryIn recent years, there has been an increasing need to assess near-surface geological risks in coastal areas in Japan. As an example, offshore wind power generation projects are rapidly being promoted by the public and private sectors, and the improvement of geotechnical methods to accurately identify and quantify the geological risks of wind turbine foundations is an urgent issue. From a geotechnical engineering perspective, it is important to visualize sub-seafloor structures down to the engineering bedrock and extract hazardous features such as active faults, submarine landslides, fluid flows, and soft sediments like buried channel fills. High-resolution seismic survey (HRS) is the most effective method to investigate detailed subseafloor structures in shallow waters, where the conventional MCS surveys are difficult to operate. The 3D visualization based on seismic attribute analysis is useful for geological risk assessment in areas where no borehole data exist. To make AVO anomaly map and detailed Holocene thickness distribution map in geotechnical investigation stage can reduce the risk of geohazard in marine development. 3D-HRS is expected to be applied in various fields, including offshore wind farm, cable route surveys, offshore site surveys, earthquake disaster prevention, CCS, deep underground nuclear waste disposal, and hydrocarbon or seabed mineral exploration.
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Inversion of Near-Surface S-wave Velocity Model Using Dispersion Curve of Surface Wave and Micro Motion Data
More LessSummaryWe proposed a new procedure ‘zoning modeling and linear transition’ to invert dispersion curves of surface wave and micro motion signal for near-surface S- velocity model. A set of three-dimensional near surface field dataset collected in a research area of southwestern China is used to illustrate the feasibility of our procedure, the subsurface S- wave velocity in this area is obtained and valid in further static correction step.
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Experimental Investigation of the Sand Production Process with the Usage of CT Scan Technology
More LessAuthors K. Batkuldinova, M.Y. Zhao, N. Hop Minh, A. Shabdirova, O. Sayakov and B. KalzhanSummaryThis research includes an investigation of sand production behaviour among different experimental conditions in the macro-scale sample. Experiments were carried out in the specifically designed HPCS and further analysed with a Computer Tomograph. CT scan results for the intact and multi-phase flow experiment specimens are included. During the experimental process, channelling was observed, which requires further investigation. The observed channelling collocates with the numerical model results obtained in the research group.
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Submarine Stratigraphy and Structures in the Singapore Strait based on Single-Channel Seismic Reflection and Multibeam Bathymetry
More LessAuthors A.M. Surya Nugraha, S. Chua, A. Green, U. Schattner, Y. Yu Ting, D. Slogrove and A. SwitzerSummaryNew single-channel high-resolution seismic reflection and multibeam bathymetry data allow a detailed study of the stratigraphy and tectonics of the underexplored Singapore Strait. The data collected aboard the R/V Galaxea during a dedicated 9-day survey (March 2023) reveal the seabed relief, sub-bottom morphologies, Late Quaternary sediment distribution, and underlying bedrock structure. Data show significant structural and stratigraphic contrasts between the western and eastern regions of the Singapore Strait. The folded and faulted bedrocks commonly observed in the west are associated with the Middle Triassic Jurong and Upper Triassic Sentosa groups. In the eastern region, seismic data reveals a network of buried incised channels that record late Quaternary glacial and interglacial environmental and sea-level changes at the core of the Sunda Shelf. Our results uncover unknown chapters in the evolution of the Singapore Strait and, more specifically, the stratigraphic development of Sundaland.
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Modeling of Air-Coupled Surface Waves and its Implications for Non-Contact Seismic Testing
More LessSummaryIn this study, we successfully derived, modeled, and verified the full-wave response of air-coupled surface waves for non-contact seismic testing. The modeling results indicate that there is no noticeable loss of wave propagation modes when transitioning from surface displacement to air pressure. The capability to accurately and efficiently model the full-wave information eliminates the need to extract apparent modes from the air-coupled measured dispersion spectrum and assume Lamb mode approximation for data interpretation. By fitting the predicted experimental FVS to the measured one, model compatibility and higher model constraints can be achieved in the inversion. In this abstract, we only focus on the theoretical modeling part, the applicability and performance of our solution for pavement inspection will be tested in real sites and reported in the future.
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Labscale Experiment Fluid Injection Using Self Potential, Electrical Resistivity Tomography, and Mise-à-la-Masse
More LessSummaryFluid distribution mapping in the fluid injection process of oil field development is a significant challenge in the oil and gas industry. Therefore, a cost-efficient and accurate monitoring method is required. This paper describes the use of one of the geophysical methods, the electrical method, to map fluid movement in a more efficient cost compared to other methods. The laboratory experiment was conducted using soil as the cap rock and quartz sand as the reservoir rock. The Self Potential (SP) and Electrical Resistivity Tomography (ERT) methods show the presence of water fluid in the pool tank. Meanwhile, the measurement results of the ERT method using the Multigradient configuration when there is water injection with a flow rate of 1 L/m and a north-south direction obtained a resistivity value of about 0–30 Ωm. In general, the water injection system equipped with monitoring capabilities for controlling the injection flow rate improves overall experimental precision. The result of this study can be extended into a field scale study to directly monitor the subsurface fluid distribution.
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Full-Wavefield Surface Wave Method for Pavement Inspection
More LessSummaryAssessing the stiffness of roads during construction and maintenance is a crucial field of study with a significant impact on daily human life. The multichannel analysis of surface wave method can provide shear wave velocity (VS) information, which correlates with material stiffness. In comparison to typical geotechnical seismic surveys, the survey configuration for pavement is on a smaller scale, and the examined frequency range is also higher than in geotechnical site investigations. However, the measured dispersion curve may not be dominated by the fundamental mode (FM) in the higher frequency range; as a result, FM inversion is not applicable in such a high-frequency range. In this scenario, frequency-velocity spectrum (FVS) inversion based on full-wavefield computation proves advantageous, eliminating the need to identify the mode or wave type. A synthetic pavement structure is selected to examine the performance of FVS inversion through Monte Carlo search. The final inverted result provides an accurate estimation of the true VS profile, showing great potential for pavement inspection.
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Multiple Linear Array Microtremor Measurement Across the Nagao Fault
More LessAuthors K. ChimotoSummaryWe performed 18 linear arrays using 6 recorders simultaneously with high-sensitivity seismometer along the survey line which crosses an active fault, Nagao fault in Kagawa Prefecture, Japan. The survey line was set as the same line with that the seismic reflection survey have been conducted. We computed H/V, single-station cross-correlation and phase velocity using cross-correlation by zero-crossing method. The contour map of H/V shows significant variation of peak frequency at the expected fault location. The single-station cross-correlation and phase velocity also showed a variation at the fault location. It suggests a potential for the use of microtremors for the exploration of fault location with low-cost than seismic survey method.
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Integrated Study of Natural Fracture Reservoir WFH Oil Field in Banggai Basin
More LessAuthors R. Armanda, D. Yusmen, B. Sapiie and I. GunawanSummaryThe results of the fracture orientation modeling in the WFH field using the elastic dislocation method show a relatively northeast-southwest direction with a slope of 34–65 degrees. High intensity fractures are concentrated in the maximum curvature of the structures in the WFH field and are associated with fault planes with high displacement values. The slip tendency modeling indicates that several fracture zones have entered a critical zone (critically stressed fracture). Based on the dilation tendency modeling carried out there are several fracture zones with high values which indicate the tendency for the fractures to be more open and have the ability to transmit hydrocarbons. The integration of the productive zone with the production speed provides a positive correlation where wells that penetrate the productive zone with trajectories that are relatively parallel to the direction of the critical fracture will provide a greater production rate in this field.
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Prediction of Long-Period Ground Motion during the 2019 Central Luzon Earthquake in the Philippines
More LessAuthors R. Grutas, K.R. Pasoquen, M.W. Andaya and H. YamanakaSummarySimulations of the fault rupture within the fault system were calculated using the parameters of the 2019 M6.1 Zambales earthquake and were compared to actual strong motion data. A fault model of the East Zambales Fault, which traverses the eastern side of the Zambales Range, was used in the simulation. By using the results of microtremor array measurements at different locations, we limit the structure velocity model applied in our calculations. In order to compare the results of actual strong motion data to the simulations, the coordinates of nine strong motion stations around the vicinity were selected and were used as coordinates for the peak ground motions of the simulations. The methodology used assesses the long-period ground motion that originates from a finite fault source model consisting of multiple asperities embedded in a velocity structure. The comparison of the actual strong motion data to the simulated earthquake scenario of the M6.1 earthquake in Zambales shows that the arrival time and peak of their velocity and acceleration response spectra are comparable. The results can be used as input data to evaluate the effects of deep underground soil layers and to calculate the soil response at different sites in Zambales during earthquakes.
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Review of Excavatability Assessment Techniques in Geotechnical Engineering Practice
More LessAuthors J. Sugawara and K. SutoSummaryRock excavation is often the part of the project that leads to the greatest cost overruns, variation claims, arbitration or even litigation ( Braybrooke 1988 ). To minimise this risk, it is prudent that geotechnical/geological and geophysical outputs are calibrated each other for better definition of subsurface ground conditions. Each excavation assessment technique has its own set of pros and cons as shown in the above example. Care must be taken when dealing with the rockfill and the rock mass which consists of hard (or stronger) rock with large void since the conventional excavatability assessment techniques may overestimate the excavatability requirements.
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On the use of Time Series to Improve Signal Processing of Electrical Data
More LessAuthors J. Deparis, J. Gance and O. LeiteSummaryElectrical Resistivity Tomography (ERT) has become widely used for engineering and environmental applications in the last couple of decades due to (1) the simplification and automating of resistivity meters and (2) the new generation of inversion software. Although the initial domain of application remain relevant today, these techniques are increasingly used for deep investigation and shallow environmental/geotechnical applications. These new applications involve working with complex resistivity, which can be measured in the time domain (TDIP: Time Domain Induce Polarization) or frequency domain (SIP: Spectral Induce Polarization).
The new algorithm could process data in time and frequency domain. The first step is to estimate the no linear self-potential in order to remove it. Second step is to compute resistivity and chargeability in time or frequency domain. The results show that the improvement of the processing is weak for the resistivity and for no noisy data but we have a better estimation of chargeability. The correlation highlight a good correlation between calculated out-phasing (in frequency domain) and chargeability (in time domain).
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