Bokani Nthaba, E. Shemang, E. Atekwana, A. Selepeng
We investigated the internal structure of the Lotsane Dam for zones that may be prone to seepage and internal erosion using the electrical resistivity imaging (ERI) and the frequency domain electromagnetic (FDEM) methods. Time-lapse ERI measurements were also made for a period of 8 months in order to monitor the temporal evolution of defective zones. Results from both the FDEM and ERI measurements show two main layers. The first is an upper conductive layer varying in thickness from 10 to 25 m which is related to the clay core embankment. Situated beneath this upper conductive layer is a highly resistive crystalline basement on which the dam was founded. Furthermore, the ERI and FDEM measurements revealed the presence of fractures and possible zones of weakness within the dam foundation. Time-lapse ERI measurements revealed resistivity increases in the observed possible defective zones, including proximal to the spillway and at the embankment-foundation interface. The long-term resistivity variation may be indicating change in material properties in those portions of the dam, and may evolve to destabilize the structural integrity of the dam and or develop into preferential seepage pathways with time. The identified anomalous zones are good indicators that the embankment integrity is at risk and we suggest continuous geophysical monitoring of Lotsane Dam structure in order to ensure dam safety and integrity on the long term.
{"title":"Investigating the Earth Fill Embankment of the Lotsane Dam for Internal Defects Using Time-lapse Resistivity Imaging and Frequency Domain Electromagnetics","authors":"Bokani Nthaba, E. Shemang, E. Atekwana, A. Selepeng","doi":"10.32389/jeeg19-057","DOIUrl":"https://doi.org/10.32389/jeeg19-057","url":null,"abstract":"We investigated the internal structure of the Lotsane Dam for zones that may be prone to seepage and internal erosion using the electrical resistivity imaging (ERI) and the frequency domain electromagnetic (FDEM) methods. Time-lapse ERI measurements were also made for a period of 8 months in order to monitor the temporal evolution of defective zones. Results from both the FDEM and ERI measurements show two main layers. The first is an upper conductive layer varying in thickness from 10 to 25 m which is related to the clay core embankment. Situated beneath this upper conductive layer is a highly resistive crystalline basement on which the dam was founded. Furthermore, the ERI and FDEM measurements revealed the presence of fractures and possible zones of weakness within the dam foundation. Time-lapse ERI measurements revealed resistivity increases in the observed possible defective zones, including proximal to the spillway and at the embankment-foundation interface. The long-term resistivity variation may be indicating change in material properties in those portions of the dam, and may evolve to destabilize the structural integrity of the dam and or develop into preferential seepage pathways with time. The identified anomalous zones are good indicators that the embankment integrity is at risk and we suggest continuous geophysical monitoring of Lotsane Dam structure in order to ensure dam safety and integrity on the long term.","PeriodicalId":15748,"journal":{"name":"Journal of Environmental and Engineering Geophysics","volume":"2 1","pages":"325-339"},"PeriodicalIF":1.0,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87474235","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Lachhab, El Mehdi Benyassine, M. Rouai, A. Dekayir, J. Parisot, M. Boujamaoui
The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.
{"title":"Integration of Multi-geophysical Approaches to Identify Potential Pathways of Heavy Metals Contamination - A Case Study in Zeida, Morocco","authors":"A. Lachhab, El Mehdi Benyassine, M. Rouai, A. Dekayir, J. Parisot, M. Boujamaoui","doi":"10.32389/jeeg9-067","DOIUrl":"https://doi.org/10.32389/jeeg9-067","url":null,"abstract":"The tailings of Zeida's abandoned mine are found near the city of Midelt, in the middle of the high Moulouya watershed between the Middle and the High Atlas of Morocco. The tailings occupy an area of about 100 ha and are stored either in large mining pit lakes with clay-marl substratum or directly on a heavily fractured granite bedrock. The high contents of lead and arsenic in these tailings have transformed them into sources of pollution that disperse by wind, runoff, and seepage to the aquifer through faults and fractures. In this work, the main goal is to identify the pathways of contaminated water with heavy metals and arsenic to the local aquifers, water ponds, and Moulouya River. For this reason, geophysical surveys including electrical resistivity tomography (ERT), seismic refraction tomography (SRT) and very low-frequency electromagnetic (VLF-EM) methods were carried out over the tailings, and directly on the substratum outside the tailings. The result obtained from combining these methods has shown that pollutants were funneled through fractures, faults, and subsurface paleochannels and contaminated the hydrological system connecting groundwater, ponds, and the river. The ERT profiles have successfully shown the location of fractures, some of which extend throughout the upper formation to depths reaching the granite. The ERT was not successful in identifying fractures directly beneath the tailings due to their low resistivity which inhibits electrical current from propagating deeper. The seismic refraction surveys have provided valuable details on the local geology, and clearly identified the thickness of the tailings and explicitly marked the boundary between the Triassic formation and the granite. It also aided in the identification of paleochannels. The tailings materials were easily identified by both their low resistivity and low P-wave velocity values. Also, both resistivity and seismic velocity values rapidly increased beneath the tailings due to the compaction of the material and lack of moisture and have proven to be effective in identifying the upper limit of the granite. Faults were found to lie along the bottom of paleochannels, which suggest that the locations of these channels were caused by these same faults. The VLF-EM surveys have shown tilt angle anomalies over fractured areas which were also evinced by low resistivity area in ERT profiles. Finally, this study showed that the three geophysical methods were complementary and in good agreement in revealing the pathways of contamination from the tailings to the local aquifer, nearby ponds and Moulouya River.","PeriodicalId":15748,"journal":{"name":"Journal of Environmental and Engineering Geophysics","volume":"41 1","pages":"415-423"},"PeriodicalIF":1.0,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80980260","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Underground nuclear magnetic resonance (NMR) is introduced to detect the risk of groundwater-induced disasters in the underground engineering such as tunnels and mines. However, underground NMR is in practice often limited to the extremely low signal-to-noise ratios (SNRs). On the one hand, small coils are necessary to be used to detect water in the narrow underground space, which decreases the amplitude of the excited signal. On the other hand, the weak signal is submerged in quite serious electromagnetic noise which is generated from the electrical installations. The low SNRs emphasize the importance of using an optimal post-processing strategy to obtain the reliable underground NMR data. The objective of this paper is to explain the processing of underground NMR data taking the detection of the underground river in Doumo Tunnel as an example. We have evaluated the noise condition in Doumo Tunnel and the noise level of 0.6760 nV/m2 was found in this area. At such a high noise level, the reliable underground NMR signal is difficult to be extracted and the credible depth profile of water content is unable to be provided. Then, we have analyzed the noise interference. Although de-spiking algorithm and reference-based noise cancellation method were applied to remove the major noise sources, the underground NMR signal is still invisible. There is still a lot of additive noise remained, so time-frequency peak filtering method is further used to suppress the remaining noise. The performance of the proposed post-processing strategy is tested on the underground NMR data from the underground river. The result was consistent with the geological structure, which is demonstrated to be able to directly provide a security pre-warning of the underground engineering.
{"title":"Processing of Underground Nuclear Magnetic Resonance Data for Underground River Detection: A Case Study in Doumo Tunnel, Guizhou, China","authors":"Zhang Yang, Sijia Yu, Ling Wan, Tingting Lin","doi":"10.32389/jeeg19-083","DOIUrl":"https://doi.org/10.32389/jeeg19-083","url":null,"abstract":"Underground nuclear magnetic resonance (NMR) is introduced to detect the risk of groundwater-induced disasters in the underground engineering such as tunnels and mines. However, underground NMR is in practice often limited to the extremely low signal-to-noise ratios (SNRs). On the one hand, small coils are necessary to be used to detect water in the narrow underground space, which decreases the amplitude of the excited signal. On the other hand, the weak signal is submerged in quite serious electromagnetic noise which is generated from the electrical installations. The low SNRs emphasize the importance of using an optimal post-processing strategy to obtain the reliable underground NMR data. The objective of this paper is to explain the processing of underground NMR data taking the detection of the underground river in Doumo Tunnel as an example. We have evaluated the noise condition in Doumo Tunnel and the noise level of 0.6760 nV/m2 was found in this area. At such a high noise level, the reliable underground NMR signal is difficult to be extracted and the credible depth profile of water content is unable to be provided. Then, we have analyzed the noise interference. Although de-spiking algorithm and reference-based noise cancellation method were applied to remove the major noise sources, the underground NMR signal is still invisible. There is still a lot of additive noise remained, so time-frequency peak filtering method is further used to suppress the remaining noise. The performance of the proposed post-processing strategy is tested on the underground NMR data from the underground river. The result was consistent with the geological structure, which is demonstrated to be able to directly provide a security pre-warning of the underground engineering.","PeriodicalId":15748,"journal":{"name":"Journal of Environmental and Engineering Geophysics","volume":"22 1","pages":"315-323"},"PeriodicalIF":1.0,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80205032","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ground-wire source transient electromagnetic method (GTEM) provides better investigation ability than loop source TEM at a given noise level and decay time. However, at the present time, the method still stays in the one-dimensional inversion interpretation stage. Since actual geological structures are three-dimensionally distributed, the three-dimensional electromagnetic forward and inversion are crucial for understanding the electromagnetic responses of complex geological structures. Moreover, the traditional 3D smooth inversions of geophysical data have been found to inaccurately reflect small-scale and isolated anomalies. In this study, a multinary inversion method was introduced and applied to GTEM inversions. It was found that the proposed method had the ability to enable GTEM to more accurately delineate anomalous bodies when applied to detect high-resistivity target. Then, for the purpose of avoiding the need for multiple inversion tests to determine the regularization factors, a self-adaptive scheme was proposed based on the differences between the data fitting functional and the model functional during each iteration step. It was observed that by introducing the multinary inversion with adaptive regulation, more stable and accurate inversion results were obtained. In the current study, the numerical simulation results had successfully verified that the proposed multinary inversion method had provided better resolution than the traditional inversion methods.
{"title":"Ground-wire Source TEM 3D Full Time Multinary Inversion Using Adaptive Regulation","authors":"X. Luan, Q. Di, Guoqing Xue, Bin Chen","doi":"10.32389/jeeg19-037","DOIUrl":"https://doi.org/10.32389/jeeg19-037","url":null,"abstract":"Ground-wire source transient electromagnetic method (GTEM) provides better investigation ability than loop source TEM at a given noise level and decay time. However, at the present time, the method still stays in the one-dimensional inversion interpretation stage. Since actual geological structures are three-dimensionally distributed, the three-dimensional electromagnetic forward and inversion are crucial for understanding the electromagnetic responses of complex geological structures. Moreover, the traditional 3D smooth inversions of geophysical data have been found to inaccurately reflect small-scale and isolated anomalies. In this study, a multinary inversion method was introduced and applied to GTEM inversions. It was found that the proposed method had the ability to enable GTEM to more accurately delineate anomalous bodies when applied to detect high-resistivity target. Then, for the purpose of avoiding the need for multiple inversion tests to determine the regularization factors, a self-adaptive scheme was proposed based on the differences between the data fitting functional and the model functional during each iteration step. It was observed that by introducing the multinary inversion with adaptive regulation, more stable and accurate inversion results were obtained. In the current study, the numerical simulation results had successfully verified that the proposed multinary inversion method had provided better resolution than the traditional inversion methods.","PeriodicalId":15748,"journal":{"name":"Journal of Environmental and Engineering Geophysics","volume":"102 15","pages":"403-413"},"PeriodicalIF":1.0,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72371101","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fengkai Zhang, B. Liu, Jing Wang, Li Yao, Nie Lichao, Wang Zhengfang, Chongmin Zhang
Full waveform inversion (FWI) is an advanced inversion technique for ground penetrating radar (GPR), which could provide quantitative, high-resolution subsurface imaging. FWI has been used widely to process crosshole and on-ground multi-offset GPR data, but its application to on-ground common-offset GPR data is more difficult and being developed. This is mainly because that on-ground common-offset GPR has much less coverage of the subsurface and mainly includes reflective information. The application of conventional FWI to pure reflection data in the absence of a highly accurate starting velocity model is difficult. Here, we demonstrate a means of achieving this successfully by preprocessing the observed data and the residual fields with an integral algorithm, which could produce a more reasonable gradient and therefore lead to better inversion results. Several cases verify the effectiveness of this method. We achieve the simultaneous inversion of relative permittivity and conductivity for on-ground common-offset GPR, and discuss the trade-off between permittivity and conductivity in details. According to the inversion results of test models, it seems that the inversion result of relative permittivity is more credible in most cases.
{"title":"Two-dimensional Time-domain Full Waveform Inversion of On-ground Common-offset GPR Data Based on Integral Preprocessing","authors":"Fengkai Zhang, B. Liu, Jing Wang, Li Yao, Nie Lichao, Wang Zhengfang, Chongmin Zhang","doi":"10.32389/jeeg19-052","DOIUrl":"https://doi.org/10.32389/jeeg19-052","url":null,"abstract":"Full waveform inversion (FWI) is an advanced inversion technique for ground penetrating radar (GPR), which could provide quantitative, high-resolution subsurface imaging. FWI has been used widely to process crosshole and on-ground multi-offset GPR data, but its application to on-ground common-offset GPR data is more difficult and being developed. This is mainly because that on-ground common-offset GPR has much less coverage of the subsurface and mainly includes reflective information. The application of conventional FWI to pure reflection data in the absence of a highly accurate starting velocity model is difficult. Here, we demonstrate a means of achieving this successfully by preprocessing the observed data and the residual fields with an integral algorithm, which could produce a more reasonable gradient and therefore lead to better inversion results. Several cases verify the effectiveness of this method. We achieve the simultaneous inversion of relative permittivity and conductivity for on-ground common-offset GPR, and discuss the trade-off between permittivity and conductivity in details. According to the inversion results of test models, it seems that the inversion result of relative permittivity is more credible in most cases.","PeriodicalId":15748,"journal":{"name":"Journal of Environmental and Engineering Geophysics","volume":"12 1","pages":"369-380"},"PeriodicalIF":1.0,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"87233774","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Editor's Foreword","authors":"D. Rucker","doi":"10.32389/jeeg20-998","DOIUrl":"https://doi.org/10.32389/jeeg20-998","url":null,"abstract":"","PeriodicalId":15748,"journal":{"name":"Journal of Environmental and Engineering Geophysics","volume":"129 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88326879","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We developed an artificial neural network to map the distribution of geologic conductivity in the earth subsurface using the airborne transient electromagnetic method. The artificial neural network avoids the need for complex derivations of electromagnetic field formulas and requires only input and transfer functions to obtain a quasi-resistivity image. First, training sample set from the airborne transient electromagnetic response of homogeneous half-space models with different resistivities was formed, and network model parameters, including the flight altitude, time constant, and response amplitude, were determined. Then, a double-hidden-layer back-propagation (BP) neural network was established based on the mapping relationship between quasi-resistivity and airborne transient electromagnetic response. By analyzing the mean square error curve, the training termination criterion of the BP neural network was determined. Next, the trained BP neural network was used to interpret the airborne transient electromagnetic responses of various typical layered geo-electric models, and the results were compared with that from the all-time apparent resistivity algorithm. The comparison indicated that the resistivity imaging from the BP neural network approach was much closer to the true resistivity of the model, and the response to anomalous bodies was better than that from an all-time apparent resistivity. Finally, this imaging technique was used to process field data acquired by employing the airborne transient method from the HuaYin survey area. Quasi-resistivity depth sections calculated with the BP neural network and the actual geological situation were in good.
{"title":"Resistivity-depth Imaging with the Airborne Transient Electromagnetic Method Based on an Artificial Neural Network","authors":"B. Feng, Jifeng Zhang, Dong Li, Yang Bai","doi":"10.32389/jeeg19-087","DOIUrl":"https://doi.org/10.32389/jeeg19-087","url":null,"abstract":"We developed an artificial neural network to map the distribution of geologic conductivity in the earth subsurface using the airborne transient electromagnetic method. The artificial neural network avoids the need for complex derivations of electromagnetic field formulas and requires only input and transfer functions to obtain a quasi-resistivity image. First, training sample set from the airborne transient electromagnetic response of homogeneous half-space models with different resistivities was formed, and network model parameters, including the flight altitude, time constant, and response amplitude, were determined. Then, a double-hidden-layer back-propagation (BP) neural network was established based on the mapping relationship between quasi-resistivity and airborne transient electromagnetic response. By analyzing the mean square error curve, the training termination criterion of the BP neural network was determined. Next, the trained BP neural network was used to interpret the airborne transient electromagnetic responses of various typical layered geo-electric models, and the results were compared with that from the all-time apparent resistivity algorithm. The comparison indicated that the resistivity imaging from the BP neural network approach was much closer to the true resistivity of the model, and the response to anomalous bodies was better than that from an all-time apparent resistivity. Finally, this imaging technique was used to process field data acquired by employing the airborne transient method from the HuaYin survey area. Quasi-resistivity depth sections calculated with the BP neural network and the actual geological situation were in good.","PeriodicalId":15748,"journal":{"name":"Journal of Environmental and Engineering Geophysics","volume":"6 1","pages":"355-368"},"PeriodicalIF":1.0,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86307326","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Muhammad Younis Khan, G. Xue, Weiying Chen, C. Boateng
The water burst from the Ordovician limestone underlain by the Permo-Carboniferous coal seams have potential to trigger coalmine hazards in Northern China. Therefore, it is crucial to identify and accurately map the water enrichment zones and delineate coal seams using an integrated approach based on surface TEM and subsurface wireline log information to avoid water-inrush hazard and ensure safe production of coal. We inverted surface based TEM data using 1-D Occam inversion to identify the conductive anomaly and then further quantified the zone of interest by gamma and resistivity logs. 1-D Occam inversion results show conductive zone around 370 m while higher resistivity and lower gamma ray log signatures were observed against coal seams. Groundwater inrush zone falls within the mid-range gamma ray and resistivity interval as shown on the petrophysical logs. The distinct log signatures (low gamma-ray and high resistivity values) clearly indicated coal seams at depth of 410 and 470 m and subsequently the log trends were used to distinguish between coal units and more permeable sands. The magnitude and the variability of these parameters in the borehole are attributed to the subsurface stratigraphic heterogeneity. They can be key clues for interpretation of depositional facies of coal-bearing sequence and may also be used as a constraint in characterization of groundwater enrichment zone.
{"title":"Investigation of Groundwater In-rush Zone using Petrophysical Logs and Short-offset Transient Electromagnetic (SOTEM) Data","authors":"Muhammad Younis Khan, G. Xue, Weiying Chen, C. Boateng","doi":"10.32389/jeeg18-111","DOIUrl":"https://doi.org/10.32389/jeeg18-111","url":null,"abstract":"The water burst from the Ordovician limestone underlain by the Permo-Carboniferous coal seams have potential to trigger coalmine hazards in Northern China. Therefore, it is crucial to identify and accurately map the water enrichment zones and delineate coal seams using an integrated approach based on surface TEM and subsurface wireline log information to avoid water-inrush hazard and ensure safe production of coal. We inverted surface based TEM data using 1-D Occam inversion to identify the conductive anomaly and then further quantified the zone of interest by gamma and resistivity logs. 1-D Occam inversion results show conductive zone around 370 m while higher resistivity and lower gamma ray log signatures were observed against coal seams. Groundwater inrush zone falls within the mid-range gamma ray and resistivity interval as shown on the petrophysical logs. The distinct log signatures (low gamma-ray and high resistivity values) clearly indicated coal seams at depth of 410 and 470 m and subsequently the log trends were used to distinguish between coal units and more permeable sands. The magnitude and the variability of these parameters in the borehole are attributed to the subsurface stratigraphic heterogeneity. They can be key clues for interpretation of depositional facies of coal-bearing sequence and may also be used as a constraint in characterization of groundwater enrichment zone.","PeriodicalId":15748,"journal":{"name":"Journal of Environmental and Engineering Geophysics","volume":"31 1","pages":"433-437"},"PeriodicalIF":1.0,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74919511","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
It is well known that the local geological characteristics in terms of topographic setting and the existence of soft sediments over bedrock may affect earthquake waves and cause seismic amplification. These effects are called “site effects”. Microtremors which provide an efficient practical tool for site effects estimation were recorded at 43 sites in Beni Suef City, Egypt. The recorded seismic signals were analyzed using the Horizontal-to-Vertical Spectral Ratio (HVSR) method. The targeted site parameters are the fundamental frequency ( f0) and the corresponding amplitude of seismic waves ( A0). Selected H/V curves with clear peak frequency have been inverted to infer the S-wave velocity profile of the underlying sediments. Information about subsurface sediments needed for the inversion process was extracted from available boreholes data. Moreover, the estimated values of f0 and A0 have been used for a preliminary calculation of the seismic vulnerability index ( Kg) which represents an indicator of soil liquefaction potentiality in the event of future earthquakes at the study area. The estimated H/V curves reveals significant variations in f0 and A0 parameters, reflecting variations in the soil characteristics (thickness and type) at the study area. The estimated values of f0 are (0.4–3.7 Hz), and commonly decrease from east to west. The A0 values vary from flat H/V curves (without any clear peak) at rock sites to 7.8 near to the Nile River and in the cultivated areas. The obtained velocity profiles could investigate S-wave structure down to 200 m depth. The estimated Kg varies from 10 to more than 50 μstrain/gal. The highest Kg values are noticed in the west and northwest in the study area were the soft sediments exist with considerable thickness, while the smallest Kg values are noticed in the south east where limestone and stiff soil occur near the ground surface.
{"title":"Soft Sediment Characterization using Seismic Techniques at Beni Suef City, Egypt","authors":"Ahmed M Meneisy, M.S. Toni, A. Omran","doi":"10.32389/jeeg19-069","DOIUrl":"https://doi.org/10.32389/jeeg19-069","url":null,"abstract":"It is well known that the local geological characteristics in terms of topographic setting and the existence of soft sediments over bedrock may affect earthquake waves and cause seismic amplification. These effects are called “site effects”. Microtremors which provide an efficient practical tool for site effects estimation were recorded at 43 sites in Beni Suef City, Egypt. The recorded seismic signals were analyzed using the Horizontal-to-Vertical Spectral Ratio (HVSR) method. The targeted site parameters are the fundamental frequency ( f0) and the corresponding amplitude of seismic waves ( A0). Selected H/V curves with clear peak frequency have been inverted to infer the S-wave velocity profile of the underlying sediments. Information about subsurface sediments needed for the inversion process was extracted from available boreholes data. Moreover, the estimated values of f0 and A0 have been used for a preliminary calculation of the seismic vulnerability index ( Kg) which represents an indicator of soil liquefaction potentiality in the event of future earthquakes at the study area. The estimated H/V curves reveals significant variations in f0 and A0 parameters, reflecting variations in the soil characteristics (thickness and type) at the study area. The estimated values of f0 are (0.4–3.7 Hz), and commonly decrease from east to west. The A0 values vary from flat H/V curves (without any clear peak) at rock sites to 7.8 near to the Nile River and in the cultivated areas. The obtained velocity profiles could investigate S-wave structure down to 200 m depth. The estimated Kg varies from 10 to more than 50 μstrain/gal. The highest Kg values are noticed in the west and northwest in the study area were the soft sediments exist with considerable thickness, while the smallest Kg values are noticed in the south east where limestone and stiff soil occur near the ground surface.","PeriodicalId":15748,"journal":{"name":"Journal of Environmental and Engineering Geophysics","volume":"5 1","pages":"391-401"},"PeriodicalIF":1.0,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73082169","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Kamaleswaran Sadatcharam, D. Altdorff, Adrian Unc, M. Krishnapillai, L. Galagedara
Apparent magnetic susceptibility (MSa) as recorded by electromagnetic induction (EMI) instruments could offer relevant information about non-soil subsurface features. It is less affected by natural soil properties than its prominent counterpart, i.e., apparent electrical conductivity (ECa). Hence, MSa is generally a promising approach to investigate artificial inclusions and structures in soil. However, while the origin depth of EMI based ECa is widely accepted, the depth sensitivity (DS) of MSa measurements remains poorly understood. The depth interpretation of MSa is particularly challenging due to negative values especially for objects that are randomly distributed over different depths. Here we assessed the performance of both multi-coil (MC) and multi-frequency (MF) EMI sensors for identifying and determining the DS of MSa measurements in shallow soils through detection of buried small targets of known conductivity. Two experiments were conducted in a sandy loam podzolic soil in western Newfoundland, Canada. Materials of different conductivities, including metal and plastic targets, were buried at depths between 20 and 80 cm. Three inter-coil separations (32, 71 and 118 cm) of the MC sensor and four factory-calibrated frequencies (18, 38, 49 and 80 kHz) of the MF sensor were tested in both horizontal and vertical coil orientations. The MC sensor clearly detected all four metal targets from three coil separations in both coil orientations while the MF sensor identified more anomalies than targets limiting its information value. Based on the measurements from MC and the theoretical DS function, a criterion was developed and validated to assess the potential depth origin of MSa. We found that negative or less than the background values occur, if the depth of the target is shallower than 0.36 times the coil distance of the employed EMI sensor. According to this criterion, the depth origins of metallic targets were correctly identified under the assumption of low induction numbers, even if values were negative.
{"title":"Depth Sensitivity of Apparent Magnetic Susceptibility Measurements using Multi-coil and Multi-frequency Electromagnetic Induction","authors":"Kamaleswaran Sadatcharam, D. Altdorff, Adrian Unc, M. Krishnapillai, L. Galagedara","doi":"10.32389/JEEG20-001","DOIUrl":"https://doi.org/10.32389/JEEG20-001","url":null,"abstract":"Apparent magnetic susceptibility (MSa) as recorded by electromagnetic induction (EMI) instruments could offer relevant information about non-soil subsurface features. It is less affected by natural soil properties than its prominent counterpart, i.e., apparent electrical conductivity (ECa). Hence, MSa is generally a promising approach to investigate artificial inclusions and structures in soil. However, while the origin depth of EMI based ECa is widely accepted, the depth sensitivity (DS) of MSa measurements remains poorly understood. The depth interpretation of MSa is particularly challenging due to negative values especially for objects that are randomly distributed over different depths. Here we assessed the performance of both multi-coil (MC) and multi-frequency (MF) EMI sensors for identifying and determining the DS of MSa measurements in shallow soils through detection of buried small targets of known conductivity. Two experiments were conducted in a sandy loam podzolic soil in western Newfoundland, Canada. Materials of different conductivities, including metal and plastic targets, were buried at depths between 20 and 80 cm. Three inter-coil separations (32, 71 and 118 cm) of the MC sensor and four factory-calibrated frequencies (18, 38, 49 and 80 kHz) of the MF sensor were tested in both horizontal and vertical coil orientations. The MC sensor clearly detected all four metal targets from three coil separations in both coil orientations while the MF sensor identified more anomalies than targets limiting its information value. Based on the measurements from MC and the theoretical DS function, a criterion was developed and validated to assess the potential depth origin of MSa. We found that negative or less than the background values occur, if the depth of the target is shallower than 0.36 times the coil distance of the employed EMI sensor. According to this criterion, the depth origins of metallic targets were correctly identified under the assumption of low induction numbers, even if values were negative.","PeriodicalId":15748,"journal":{"name":"Journal of Environmental and Engineering Geophysics","volume":"23 1","pages":"301-314"},"PeriodicalIF":1.0,"publicationDate":"2020-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72971060","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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