bluuebunny/crossref_metadata_2025 huggingface dataset:
High-resolution P- and S-wave Seismic Reflection Followed by Engineering Modeling for Geotechnical Site Characterization in Southern Illinois
Authors: Ismail Ahmed , Abdelnaby Adel , Larson Timothy
Published: December 2020

A study was conducted to determine whether the structural failure of a house in a residential subdivision in southern Illinois was caused by the collapse of an old underground coal mine ( i.e. mine subsidence) or as a result of a landslide. The house was displaced approximately 5 m downhill towards an engineered lake behind it. To detect any old mines near the house, we acquired high-resolution S-wave seismic reflection profiles along the roads surrounding the subdivision and a series of high-resolution P-wave reflection profiles in the immediate vicinity of the house. The S-wave seismic reflection profiles imaged a strong shallow horizon that we interpreted as Pennsylvanian siltstone overlying the Mecca Quarry Shale and Colchester Coal, which had been previously mined in the area. Locally, this horizon showed no evidence of any recent mining activities. The high-resolution P-wave reflection profiles imaged a steeply dipping bedrock with a 20° dip at the house location. These results exclude mine subsidence from being the cause for the house failure. To investigate land sliding as a possible cause of the house failure, depths to bedrock from the seismic results together with the soil type information were used to model the soil materials with a Mohr-Coulomb stress-strain model. The engineering model demonstrated that a land slide is a more plausible cause for the house failure, which agrees with the seismic results.
Application of Frequency-Dependent Traveltime Tomography to 2D Crosswell Seismic Field Data
Authors: Liao Jianping , Guo Zhenwei , Liu Hexiu , Dai Shixin , Zhao Yanlin , Wang Lixin , Wang Huazhong , Hursthouse Andrew
Published: December 2020

We applied Zelt's new frequency-dependent traveltime tomography (FDTT) method to 2D crosswell seismic field data from an eastern oil field in China. The FDTT uses the frequency content in the seismic waves in both the forward and inverse modeling steps. Although FDTT only uses a 300 Hz frequency to invert the dataset, the degree of matching between the inverted layers from FDTT and that of a sonic well logging curve is high, which shows that FDTT provides a high resolution reconstruction of subsurface structure through the simple use of the first-arrival traveltime data. The case study demonstrates that the FDTT algorithm is practical and can stand up to the complexities of a real 2D crosswell dataset. Additionally, we show that the FDTT method can create a high resolution long wavelength velocity model.
Time Domain and Frequency Domain Induced Polarization Modeling for Three-dimensional Anisotropic Medium
Authors: Liu Weiqiang , Lin Pinrong , Lü Qingtian , Chen Rujun , Cai Hongzhu , Li Jianhua
Published: December 2020

Time domain induced polarization (TDIP) and frequency domain induced polarization (FDIP) synthetic models, incorporating three-dimensional (3D) anisotropic medium, were tested. In TDIP modeling, both resistivity and chargeability of the medium were anisotropic, and the apparent chargeability values were calculated by carrying out two resistivity forward calculations using resistivity with and without an IP effect. We analyzed the TDIP response of a 3D isotropic cube model embedded in the anisotropic subsurface half-space. In FDIP modeling, the complex resistivity of the medium at various frequencies was anisotropic. The complex resistivity was determined by a Cole-Cole model with anisotropic model parameters. We then analyzed the FDIP response of a 3D anisotropic cube model embedded in an isotropic subsurface half-space. Both of the TDIP and FDIP simulation results suggest that IP responses acquired in two orthogonal directions on the surface are different when the same arrays are used and acquisition in orthogonal directions helps resolve the presence of anisotropy. The anisotropy should be taken into account in practice for TDIP and FDIP exploration.
The First Fixed-wing Aircraft for Chinese Antarctic Expeditions: Airframe, modifications, Scientific Instrumentation and Applications
Authors: Cui Xiangbin , Greenbaum Jamin S. , Beem Lucas H. , Guo Jingxue , Ng Gregory , Li Lin , Blankenship Don , Sun Bo
Published: December 2020

The Antarctic Ice Sheet plays a critical role in global climate and sea level change resulting in it being the focus of international scientific exploration. Airborne platforms have been applied to study large geographical regions of Antarctica that are logistically difficult to reach by other means. For 30 years Chinese Antarctic expeditions, have widely applied ground based platforms in Antarctica. During the 32nd Chinese National Antarctic Research Expedition (years 2015/16), the first fixed-wing aircraft (Snow Eagle 601) was deployed by Polar Research Institute of China with special modifications for polar operation and airborne geophysical investigation of ice sheets. Here, the airframe of the aircraft and modifications for science operation in Polar Regions, as well as scientific instrumentation, system integration and its first application in Antarctica are introduced in detail.

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An Investigation of the Effect of Source Geometry on Grounded-Wire TEM Surveying with Horizontal Electric Field
Authors: Zhou, Nannan , Xue, Guo-qiang , Hou Dong-yang , Lu Yunfei
Published: December 2020

The grounded-wire transient electromagnetic (TEM) survey has been successfully applied in the mining industry to detect resources in the subsurface. Recently, research efforts have been devoted to developing both the theory and application of the short-offset TEM (SOTEM), which requires the layout of a line source for transmitting the electromagnetic signals. In practice, however, the terrain complexities of exploration areas, such as mountains and construction areas, often limit the layout of such linear geometry and moreover cause the source to be folded several times, which undesirably increases the computational differences especially when the line-source model is used for field data processing and interpretation. Therefore, to achieve high resolution TEM detection, it is now necessary to adapt the source layout to the local terrain. For describing the effect of source geometry on the SOTEM surveying, this study first presents a superposing-dipole approach for estimating the SOTEM field from arbitrarily-shaped sources and then qualifying the relative differences in the horizontal electric field due to varying source geometry. It is expected that such approach could be implemented for improving the TEM detection accuracy by taking into account all the turning points in a non-linear source layout, especially in the restricted areas.

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TEM Pseudo-Wave Field Extractions Using a Modified Algorithm
Authors: Li Xiu , Xue Guo-qiang , Zhi Qing-quan , Li Hai , Zhong Hua-sen
Published: December 2020

The migration of the transient electromagnetic method (TEM) has been a research topic for decades. The method, which uses the mathematical q transform to perform imaging in the wave domain, has proved its validity in some circumstances. One of the crucial steps of this kind of method is the inverse q transform, which extracts the pseudo-wave field that satisfies the wave equation from the TEM data. Conventionally, the time range of the q integral is divided into several windows and the transformation result is recovered using a regularization method, in which each window is summed up to get the final wave field. Although the recovered wave field demonstrates the key features as is indicated in the wave equation and the corresponding imaging techniques have proved to be useful, the accuracy of the extraction of these wave fields hampered the development of more accurate migration techniques. This paper will focus on the extraction of the wave field from the TEM data. A novel correlation stacking method was proposed and compared with singular value decomposition (SVD) and the pre-conditioned regularization conjugate gradient method. The comparison of the results from these methods demonstrates that the extraction results of the proposed correlation stacking method were more accurate and stable. The pseudo-seismic wave field extraction results of the actual measured TEM data showed that the correlation stacking method was the optimal method for the pseudo-seismic wave field extraction of TEM data.

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Spectral Analysis of Surface Waves with Simultaneous Fiber Optic Distributed Acoustic Sensing and Vertical Geophones
Authors: Costley R. Daniel , Galan-Comas Gustavo , Kirkendall Clay K. , Simms Janet E. , Hathaway Kent K. , Parker Michael W. , Ketcham Stephen A. , Smith Eric W. , Folks William R. , Milburn Troy W. , Wadman Heidi M.
Published: December 2020

Experiments were performed comparing the response of fiber optic distributed acoustic sensing (DAS) to vertical geophones installed on the surface. The DAS consisted of an optical interrogator attached to an optical fiber. The fiber was part of an optical cable that was installed at depths of 0.3 to 0.76 meters in a coastal environment composed of unconsolidated sand. Seismic signals generated with an impact hammer were recorded simultaneously with both systems and directly compared. Experiments were performed with two different configurations, broadside and end-fire, between the source and the fiber optic cable. The seismic signals recorded in the two configurations and with the two sensor systems were processed identically using the Spectral Analysis of Surface Wave method. The results demonstrate the suitability and limitations of using DAS for near-surface seismic measurements.
Delineation of Sedimentary Facies and Groundwater-Sea Water Disposition in an Intertidal Zone of the Bay of Bengal using GPR and VES
Authors: Layek Mrinal Kanti , Debnath Palash , Sengupta Probal , Mukherjee Abhijit
Published: December 2020

A combination of geophysical study including ground penetrating radar (GPR) and vertical electrical sounding (VES) was done to identify different shallow-subsurface depositional features in an intertidal coast of the eastern parts of India, adjoining the Bay of Bengal (BoB) (Chandipur, Odisha state). The study was aimed to understand the variation of sedimentary depositional sequences, prograding to the ocean from land, as well as towards the confluence of a river channel with the BoB. Six VES points and 85 GPR traverses were taken in the intertidal flat. The data were calibrated with sedimentary sequences retrieved from simultaneously drilled boreholes in four locations. Resistivity data clearly demonstrate the subsurface sediment layer boundaries with water saturation variability, up to 156 m below ground surface (bgs). The data suggest thickening of brackish water saturated clay layers towards the southwestern part. GPR data were capable of resolving the geometry of intertidal dunes, buried palaeo-channels, erosional surface, water table, eolian deposit of sand, and washover delta depositional features which are all present in this study area. Several erosional surfaces, related to sedimentary processes, e.g., delta overwash processes, were clearly demarcated. The study also successfully identified and visualized the saline-fresh groundwater interfaces and submarine ground water discharge (SGD) zones. Consequently, based on these data, a conceptual model of the depositional and erosional history of the sedimentation of the area, as well as the coastal hydrogeological disposition, was conceived.
Identification of Double-layered Water-filled Zones Using TEM: A Case Study in China
Authors: Xue Guoqiang , Hou Dongyang , Qiu Weizhong
Published: December 2020

At present in China, the use of the transient electromagnetic method (TEM) is emerging as a leading geophysical technique for exploration of water-filled zones in coal mines. These zones are more conductive than the host coal and are easy targets to map. However, there is a growing interest for the investigations of double-layered or multi-layered mined-out zones. Therefore, it is necessary to study the feasibility of TEM's abilities to detect double-layered, water-filled voids. In this study, the basic hydrogeological conditions of a survey area, located in the northern China, are described. The corresponding geophysical models of the single- and double-layered water-filled zones are developed from borehole logging data. Then, forward calculations of different models are carried out with 1D numerical simulations. The modeling results show that it is feasible for TEM to identify these types of targets under certain conditions, including instrument sensitivity, low resistivity for the water-filled zones, and shallower depths. Moreover, the field survey for locating double-layered water-filled zones in coal mines in the Datong region of Shanxi Province is verified by well drilling.
Geophysical Monitoring of Blast-induced Liquefaction at the Mirabello (NE Italy) Test Site
Authors: Passeri Federico , Comina Cesare , Marangoni Valeria , Foti Sebastiano , Amoroso Sara
Published: December 2020

A blast-induced liquefaction test was conducted in the surroundings of Mirabello (NE Italy), where extensive liquefaction phenomena were observed after the 2012 Emilia earthquake. This experiment is the first blast-induced liquefaction test carried out in Italy. Several geophysical investigations were performed at the site to define initial soil condition and to evaluate the variations of the geophysical parameters over time. Specifically compressional ( VP) and shear ( VS) wave velocities were measured using both invasive (down-hole) and non-invasive (surface wave) tests. Electric Resistivity Tomography (ERT) tests were also carried out. Tests results before and after the blast-induced liquefaction are here presented and discussed with respect to the observed liquefaction effects. The evolution of measured geophysical parameters suggests that the soil modifications due to blasting ( i.e., changes in porosity and soil structure) can be imaged with the adopted approaches.
Application of 3-D FKK Filtering in 3-D High-density Onshore Seismic Field Data
Authors: Liao Jianping , Fu Songyuan , Xu Yungui , Li Weibo , Chen Jianxiong , Wang Huazhong , Peng Suping , Hursthouse Andrew
Published: December 2020

For linear noise such as seismic ground roll, 3-D frequency-wavenumber-wavenumber (3-D FKK) domain filtering suppression is better than 2-D frequency-wavenumber (F-K) domain filtering. In recent years, with the continuous development of computer processing speed and memory capacity, high-density data acquisition in seismic exploration has been widely applied in the hydrocarbon industry, opening up the application of 3-D FKK filtering methods. We applied the 3-D FKK filtering software to a 3-D high-density onshore seismic field dataset from a coal mine in western China. The case study demonstrates that the linearity of the noise in the field data is better represented by constructing the single shot records as a minimum dataset. Both theoretical synthetic models and the 3-D high-density onshore seismic field data numerical filtering experiments demonstrate that the feasibility of 3-D FKK filtering.
Influence of GNSS Receivers on GPR Results
Authors: Tanajewski Dariusz , Popielarczyk Dariusz , Ciecko Adam
Published: December 2020

Even though satellite positioning has been used in ground penetrating radar (GPR) measurements for years, there are no studies ruling out the influence of modern satellite positioning receivers on the operation of GPR antennas. In order to rule out mutual influence between devices, a field study was carried out to determine the possible influence of a Global Navigation Satellite Systems (GNSS) receiver on the results obtained from GPR. To this end, several equipment combinations based on two receivers were compared. This was followed by a numerical analysis of selected samples from the recorded data sets. The following were calculated: average values of signal amplitudes, their standard deviations and the signal-to-noise ratio, coefficient of variation, and signal stability parameters. We also suggested using a modified standard deviation based on the properties of the reference signal. Based on the results, we concluded that there were rather significant changes between the data sets for various equipment combinations, which may indicate that a GNSS receiver affects GPR data in some way. However, the influence was not significant enough to result in the qualitative misinterpretation of data.
An Innovative Use of TDR Probes: First Numerical Validations with a Coaxial Cable
Authors: Persico Raffaele , Farhat Iman , Farrugia Lourdes , D'Amico Sebastiano , Sammut Charles
Published: December 2020

In this paper we propose a study regarding some possibilities that can be offered by a time domain reflectometry (TDR) probe in retrieving both dielectric and magnetic properties of materials. This technique can be of interest for several applications, among which the characterization of soil in some situations. In particular, here we propose an extension of the paper “Retrieving electric and magnetic propetries of the soil in situ: New possibilities”, presented at the IWAGPR, held in Edinburgh in 2017, and as a new contribution we will validate a transmission line model with numerical data simulated by the CST code.
Measurement of Bulk Electrical Properties Using GPR with a Variable Reflector
Authors: Redman J. David , Annan A. Peter , Diamanti Nectaria
Published: December 2020

Bulk electrical properties of media are important inherently for ground penetrating radar (GPR) applications and for providing a means to determine indirectly other physical properties such as moisture content. We have developed a reflector whose reflectivity can be controlled electronically. This variable reflector controlled by a GPR provides an effective method to measure bulk electrical properties of media. For sample measurements, the GPR is placed on one side of a sample and the variable reflector on the opposite side. GPR trace data are then acquired with the reflector in an on-state and in the off-state. By differencing these measurements, we improve the ability to detect the specific reflection event from the variable reflector. This process removes both the direct wave and clutter from the trace data, improving the quality of the refection event and our ability to accurately pick its arrival time and amplitude. We describe the variable reflector, a prototype instrument based on the reflector and numerical modeling performed to understand its response. We also show the results of testing applications to the measurement of wood chip moisture content and monitoring of the electrical properties of concrete during the curing process.
Polarization Migration of Multi-component Seismic Data for Survey in the Tunnel of Mountain Cities
Authors: Wang Bo , Huang Lanying , Liu Shengdong , Zhou Fubao , Jin Biao , Sun Huachao , Zhang Heng
Published: December 2020

With the development of transportation in the west of China, tunnel construction in mountain cities is becoming very important and widespread. Tunneling safety in the tunnels is usually controlled by faults, and the advanced prediction of faults by seismic detection method has become a research hotspot in the field of engineering geophysics. Unlike seismic exploration on the ground, the sources and receivers are not properly arranged due to the limitation of the tunnel detection space, so as to cause migration artifacts problem in the process of advanced migration imaging. The problem results in inaccurate imaging of the faults. To solve the problem, this paper proposed a new polarization migration method. The method makes use of the polarization characteristic of three-component seismic signals. The principal polarization direction is calculated by Hilbert transform and complex covariance matrix analysis. A weighted function of the principal polarization direction factor is incorporated into the migration calculation. To verify the effectiveness of the polarization migration method, this paper carries out numerical simulations. Test results demonstrate that the artifacts are eliminated by the polarization migration, and occurrence parameters of faults, such as dip and trend are calculated accurately. The field detection case shows that seismic advanced prediction which is based on polarization migration provided parameters of faults in the front of the tunnel face with 100m, and the distance error is less than 2m, and the dip error is less than 3°, which ensures efficient and safe construction of tunneling.
An Array Source TEM Apparent Resistivity Conversion and Differential Conductivity Imaging Method and its Potential Applications
Authors: Qi Zhipeng , Li Xiu , Zhang Yingying , Li He , Sun Naiquan
Published: December 2020

In this study, for the purpose of accurately detecting fissured disaster sources and diversion channels during tunnel construction, an array source transient electromagnetic device is proposed. Then, an apparent resistance conversion method and an approximate inversion algorithm for the proposed transient electromagnetic device are presented. First, a finite-difference time-domain (FDTD) method is used for the forward modeling of the proposed array source transient electromagnetic device, and the electromagnetic responses of the cracks and water-conducting channels are obtained. When compared with the transient electromagnetic square responses of the traditional loop sources, it is found that the data confirmed that the responses to the anomalies of the proposed array source transient electromagnetic device are more apparent. Then, the transformation from the array source transient electromagnetic field to the apparent resistivity is realized according to the principle of inverse function. In order to clearly identify the boundaries of the targeted anomalous bodies, a multi-source S-inversion algorithm is used to realize the array source transient electromagnetic differential imaging. The method is validated using a theoretical model. It was determined that the results of the differential imaging had effectively identified the boundaries of the anomalous bodies, and the apparent resistivity imaging had successfully determined the resistivity distributions of the anomalous bodies. Furthermore, a combination of the aforementioned methods is used to effectively identify the faults and water-flowing fractures in the model. This study's proposed algorithm was applied to the actually measured data, and the interpretation results were found to be consistent with the excavation results, which fully demonstrated the feasibility of the proposed method.
The Application of CRU-Resistivity Meters for Groundwater Investigation in Chantaburi, Thailand
Authors: Pairojn Pithan
Published: December 2020

This research proposes an investigation of groundwater by using 2D electrical resistivity techniques with the low-cost Chandrakasem Rajabhat University Resistivity Meter (CRU-Resistivity Meter) and processing with the Chandrakasem Rajabhat University Resistivity Images software (CRU-Resistivity Images). The resistivity meter, constructed of parts costing less than $1,000 USD, was tested at Soi Dao in Chantaburi, Thailand with a profile length of 90 m. Using a Wenner electrode array, the results showed that high resistivity zones greater than 100 ohm-m at a depth of 8 m generally considered to be topsoil with sand. Through testing, it was also found that low resistivity zones about 10 ohm-m at a depth of 20 to 50 m depth were generally considered a suitable subsurface range for good quality groundwater. The results of total dissolved solid (TDS) from water samples confirmed that groundwater at the sites of this example survey may be used for agriculture.
The Simulation of Transient Electromagnetic Based on Time-domain IP Model
Authors: Zhou Lei , Yan LiangJun , Kachaje Osborne , Xie Xingbing , Mao Yurong , Zhang Haoran
Published: December 2020

When transient electromagnetic investigation methods are carried out in the field, the measured data often contain both the induced polarization (IP) effect and the electromagnetic effect. In order to study the IP effect in the transient electromagnetic response, many researchers first calculate the electromagnetic field which considers the IP effect by replacing traditional resistivity with complex resistivity of the Cole-Cole model in the frequency domain. After the forward modeling calculation of the electromagnetic field in the frequency domain that considers the IP effect, the transient electromagnetic field in time-domain is obtained by a time-frequency transform algorithm. In this paper, the resistivity is directly replaced by the time-variant resistivity expression of the Cole-Cole model by using digital filter algorithms when we simulate the transient electromagnetic fields in time- domain. The calculated result of the Cole-Cole model in time-domain and in frequency-domain are consistent with each other, as observed in the horizontal electric field and the vertical magnetic field comparisons, which indicates the correctness of the numerical computation method adopted in this paper. The research presented herein allows us to observe the influence of the IP effect on transient electromagnetic field as well as study the mechanisms of IP directly.
Assessment of Chromium Waste Contamination by Electrical Resistivity Tomography: A Case Study
Authors: Wang Yuling , Xu Ya , Nai Changxin , Dong Lu
Published: December 2020

This study aims to determine the chromium contamination at an abandoned chemical factory by electrical resistivity tomography (ERT). Five ERT survey lines were conducted in the main production plant and two boreholes were drilled to collect soil samples for soil analysis. The 2D and 3D resistivity model were constructed to evaluate the pollution plumes. The ERT results showed that seven low-resistivity zones are observed in the 2D resistivity profiles, which may indicate the main pollution areas at the site. The 3D electrical resistivity model further showed that the soil pollution is more severe in the southwest than in the other areas of the site. The ERT results were partly verified by chemical analysis of soil samples. These ERT results can be further used for additional designs of soil and groundwater sampling.
Shallow Seismic Reflection Investigation of Unstable Sedimentary Deposits in the Dăneasa Area, Romania
Authors: Panea Ionelia
Published: December 2020

Results of shallow seismic reflection measurements, performed over an area with unstable sedimentary formations in the near subsurface, are presented. The investigated area is located on the Olt Valley, in the vicinity of the Dăneasa village, Romania, crossed by a railway line and a national road on which the traffic is very intense. Data were collected along a linear profile, with a length of 94 m, perpendicular to the railway line and the national road using a fixed spread of 48 vertical-component geophones with the sources rolling along the acquisition line. The surface waves generated by the intense traffic on the national road interfered with the seismic arrivals seen on most of shot gathers, especially with those seen on the traces from receiver locations greater than 48 m. The interrupted continuity of two shallow reflectors, R1 and R2, seen on the depth-converted seismic section at depth values shallower than 30 m, could be interpreted as an effect of the presence of two steep failure planes deveIoped into the ground. A P-wave velocity-depth model down to a depth of 20 m after first-arrival traveltime tomography was then created, on which four sedimentary layers with variable thicknesses and constant velocities, separated by the interfaces L1, L2 and L3, were interpreted. By comparing the depth-converted seismic section with the P-wave velocity-depth model, the reflectors R1 and R2 on the seismic section correspond pretty well with the interfaces L2 and L3 from the velocity-depth model.
Conceptualizing Groundwater-Surface Water Interactions within the Ogallala Aquifer Region using Electrical Resistivity Imaging
Authors: Koehn Weston J. , Tucker-Kulesza Stacey E. , Steward David R.
Published: December 2020

Dynamic interactions between rivers and aquifers are controlled by the underlying hydrogeologic environment, as well as the type of hydrologic connection between the riverbed and saturated zone. The Arkansas River supplies groundwater to a heavily exploited region of the Ogallala Aquifer across Western Kansas. Site characterizations of this region using existing well and borehole data reveal large scale geologic features that significantly impact recharge processes, such as the Bear Creek fault. However, the existing hydrogeologic data do not provide the level of detail needed to fully understand the contribution of the losing river system to Arkansas Alluvial aquifer recharge. Knowledge about riverbed hydrogeology is acquirable using electrical resistivity imaging (ERI) surveys. ERI surveys and soil sample analysis were conducted at three sites along the Arkansas River to characterize the hydrogeologic environment within the Arkansas River Alluvial aquifer, which overlies the Ogallala aquifer. Temporal changes in electrical resistivity served as an indicator of the hydrologic response of the alluvial sediments to changes in river discharge as different patterns of water movement from the Arkansas River to Arkansas River Alluvial aquifer were observed. The ERI surveys revealed both fully connected and disconnected regions between the riverbed and groundwater table. The results supplement the existing geologic characterization of this region, and provide a more spatially detailed view of the hydrogeologic environment that has a direct causative effect on groundwater surface water interactions. Understanding the behavior of river-aquifer interactions is vital to the ability to predict the future holds of this important groundwater system.
Characterization of Subsurface Cavities using Gravity and Ground Penetrating Radar
Authors: Abdullah Fathi M.S. , Al-Shuhail Abdullatif A. , Sanuade Oluseun A.
Published: December 2020

Subsurface cavities occur naturally by dissolution of carbonates and evaporites or by human action, such as the construction of tunnels and tombs. They can be filled with air, water, sediments, or a combination. Gravity and ground penetrating radar (GPR) methods have been used widely to determine the location and size of subsurface cavities. The objective of this study is to present a quantitative approach to estimate the porosity and water saturation of cavity-filling materials from GPR and gravity measurements. The approach uses appropriate rock-physics models of the dielectric permittivity and density of a shallow cavity and estimates the porosity and water saturation inside the cavity by solving the two model equations simultaneously for these two variables. We test the proposed method using synthetic GPR and gravity data sets corresponding to three spherical-cavity models: air-filled, water-filled, and a partially-saturated sand filling. Results show that the method is accurate in retrieving the correct porosity within 0.76% error and water saturation within 2.4% error. We also apply the method on three published case studies over air-filled rectangular cavities. We found that the proposed method estimated the correct porosity and water saturation in one study but failed with the other studies. However, when the procedure was repeated with gravity values calculated from parameters reported in these studies, the proposed method estimated the correct porosity and water saturation accurately.
Power Density Distribution in Subsurface Fractures Due to an Energized Steel Well-casing Source
Authors: Beskardes G. Didem , McAliley W. Anderson , Ahmadian Mohsen , Chapman David T. , Weiss Chester J. , Heath Jason E.
Published: December 2020

Robust in situ power harvesting underlies the realization of embedded wireless sensors for monitoring the physicochemical state of subsurface engineered structures and environments. The use of electromagnetic (EM) contrast agents in hydraulically fractured reservoirs, in coordination with completion design of wells, offers a way to transmit energy to remotely charge distributed sensors and interrogate fracture width, extent, and fracture-stage cross-communication. The quantification of available power in fracture networks due to energized steel-cased wells is crucial for such sensor designs; however, this has not been clarified via numerical modeling in the limit of Direct Current (DC). This paper presents a numerical modeling study to determine the EM characteristics of a subsurface system that is based on a highly instrumented field observatory. We use those realistic field scenarios incorporating geometry and material properties of contrast agents, the wellbore, and the surrounding geologic environment to estimate volumetric power density near the wellbore and within hydraulic fractures. The numerical modeling results indicate that the highest power densities are mainly focused around the wellbore excited by a point current source and the fracture boundary. Using DC excitation, the highest power density in the fracture is at the fracture tip. The relatively high-power density on the order of tens of mW/m3 at the vicinity of the wellbore and at fracture tips suggests that remote charging of sensor devices may be readily possible. Simulation results also show that the region of the highest power density can be significantly increased when the EM source is located inside a conductive fracture, which may lead to a promising deployment strategy for embedded micro-sensors in geologic formations.
Geoelectrical Characterization of the Al-Kawamil New Settlement, Sohag, Egypt
Authors: Mohammed Mohammed A. , Abudeif Abdelbaset M.
Published: December 2020

Electrical resistivity tomography (ERT) is one of the most effective geophysical methods used to acquire detailed pictures of subsurface conditions without drilling. Site investigation using two- and three-dimensional electrical resistivity imaging is now a fundamental step before the design and construction of campus buildings at the University of Sohag in Egypt. In this study, an ERT survey was implemented at two pre-defined sites with the aim of selecting the most favorable location for construction of a new educational building on the university campus. The resistivity results were confirmed with boreholes drilled at both sites. RES2DINV and RES3DINV software were used for data processing and interpretation. The results show that the near surface sedimentary succession beneath both sites consists of four geoelectrical and lithological units. From the surface to a depth of 20 m, these layers are: unit 1) unconsolidated boulders and gravels intercalated with percentages of sand and reddish clay; unit 2) fine crushed calcareous gravels and sands with clays intercalations; unit 3) dry sand and clayey sand; and unit 4) shale, at the base. According to an evaluation of the presence and abundance of shale and sand contents cracks, fissures and faults, the second site is identified as more suitable for construction.
Application of Grounded Electrical Source Airborne Transient Electromagnetic (GREATEM) System in Goaf Water Detection
Authors: Li Dongsheng , Tian Zhongbin , Ma Yulong , Gu Jiayue , Ji Yanju , Li Suyi
Published: December 2020

Since goaf water can cause water inrush, collapse or other severe geological hazards in coal mining, its detection has become a significant issue. As the grounded electrical source airborne transient electromagnetic (GREATEM) system can provide considerable prospecting depth, lateral resolution, and high detection efficiency, the method may be suitable for goaf water detection. To verify the feasibility, a field electromagnetic survey over Qinshui coal mine (Shanxi province, China) was conducted, and the system was used to detect the geoelectric characteristics of goaf water. After data acquisition, data processing, and apparent resistivity calculation, the resistivity profile of survey area is clearly presented, which is consistent with the information provided by Shanxi Coal Geology Geophysical Surveying Exploration Institute, China. The result shows that the application of GREATEM system is an effective technique for resistivity detection of goaf water, and can reduce the risks in coal mining.
Application of Borehole Radar Data Processing Based on Empirical Mode Decomposition
Authors: Zuo Xuzhou , Ma Chunguang , Xiao Jianping , Zhao Qing
Published: December 2020

Borehole Radar (BHR) uses ultra-wideband electromagnetic (EM) waves to image discontinuities in formations. It has been a major bottleneck to extend BHR applications to obtain a clear and high-resolution radar profile in a complex and noisy environment, which increases ambiguity in the geology interpretation. To avoid this increased ambiguity in the geology interpretation, we proposed a scheme based on the empirical mode decomposition (EMD) and complex signal analysis theory to process the BHR data with low signal to noise ratio (SNR). The scheme includes four steps. First, the original radar profile is pre-processed to avoid mode confusion and noise interference to the radar echo. Next, the EMD method is used to process a single-channel radar dataset and to analyze the frequency components of the radar signal. Various intrinsic modes of the pre-processing radar profile are also obtained by using EMD. Finally, we reconstruct the intrinsic mode profile, which contains information about the formation, calculate the complex signals of the reconstructed radar profile using the Hilbert transform, extract the three instantaneous attributes (instantaneous amplitude, instantaneous phase, and instantaneous frequency), and draw the separate instantaneous attributes profiles. This processing scheme provides both the conventional time-distance profile also in addition to the three instantaneous attributes. The additional attributes reduce ambiguity when evaluating the original radar profile and avoid the deviation relying solely on a conventional time-distance profile. An actual radar profile, which was obtained by a BHR system in a limestone fracture zone, is used to verify the effectiveness of instantaneous attributes for improving interpretation accuracy. The results demonstrate that the EMD method is superior in processing the BHR signal under a low SNR and has the capability to separate the high-low components of the radar echo effectively.
Application of Apparent Resistivity Ratio on the Interpretation of Small Central-loop TEM Survey in Areas of Conductive Overburden
Authors: Zhao Hu , Zhou Sheng , Li Rui , Xi Zhenzhu , Long Xia
Published: December 2020

Central-loop TEM sounding data are often interpretead with apparent resistivity as a function of depth. This can quickly give a qualitative understanding of the subsurface resistivity variation. However, when the resistivity contrast between anomalies and background is weak, especially when there is a conductive overburden, the apparent resistivity image is inadequate to quickly and visually identify local anomalies. As an alternative, the apparent resistivity ratios of each measured station to a reference station is proposed as a fast way to identify local conductive anomalies qualitatively. Modeling analyses are carried out on 1D layer model, 2D fault models, and a 3D prism model with conductive overburdens. The results show that the apparent resistivity ratio outperforms the apparent resistivity on intuitively reflecting the target anomaly. As an image enhancement technique, the apparent resistivity ratio performs data transformation on the original apparent resistivity data, normalizing the background response, and highlighting the anomaly. At last, the apparent resistivity ratio method is successfully applied on interpreting a small central-loop TEM survey on investigating karst structure beneath a freshwater river. It provides an alternative simple fast way for interpretation of central loop TEM measurements.
Water Detection within the Working Face of an Underground Coal Mine Using 3D Electric Resistivity Tomography (ERT)
Authors: Gao Weifu , Shi Longqing , Zhai Peihe
Published: December 2020

Controlling water in underground coal mines is an important safety consideration. There are very few methods that can detect or map water remotely within the working face of a mine. The two-dimensional (2D) electrical resistivity tomography (ERT) method is sufficient for detecting water directly above the roof and below the floor, but it fails to detect water within the internal blocks of the working face. Therefore, it is critical to develop a new acquisition methodology for mapping internally within the face given the limited space in which to work. In this paper, we apply the pole-pole array in an L-array around the working face using a modified roll-along method. The data are then inverted using commercial software. With our new methodology, abnormal areas that likely indicate excess water are delineated to provide guidance for the control of mine water.
Fault Attitude of the North Section of Huangzhuang-Gaoliying Fault at Beijing, China and Its Effects on the Ground Rupture
Authors: Zhao Shuai , Meng Yongqi , Ma Zhenning , Sun Jiajun
Published: December 2020

Worldwide, slip on earthquake faults causes numerous disasters, resulting in large losses in human life and built structures. To minimize future losses associated with earthquakes along such faults, it is important to precisely locate the faults relative to the built environment and to determine the subsurface geometry of the faults. In Beijing, China, we used shallow-depth geophysical methods to evaluate the location and subsurface geometry of the Huangzhuang-Gaoliying fault (HGF), one of the principal tectonic faults of Beijing area. We used seismic reflection and refraction tomography, multi-channel analysis of surface waves (MASW), and paleoseismic trenching to characterize the north section of HGF near the Gaoliying section of Beijing. Our seismic images indicated that there are at least two strands of the HGF that are distributed over an approximately 200-m-wide zone. We identified a principal fault strand (F1) that is observed in all the seismic images, as well as in a paleoseismic trench. The F1 strikes approximately N49°E and dips southeastward at 70° to 75°. Over the past few years, surface ruptures have occurred along the HGF in several locations, but it is unclear if the surface ruptures were the result of tectonic slip on the HGF or were related to land subsidence along the fault.
Response Characteristics of Water-Bearing Goafs for Surface-to-Underground Transient Electromagnetic Method
Authors: Jiang Zhihai , Liu Lian , Liu Shucai , Yue Jianhua
Published: December 2020

Many of most serious disasters in coal mines around the world are attributed to underground flooding from water-bearing goafs. To ensure the operational safety in the deeper coal seams, water-bearing goafs must be clearly mapped to prevent water inrush accidents. Existing geophysical methods cannot fully meet this requirement. Building on the merits of the transient electromagnetic method (TEM) at the surface and in the mine, we propose a surface-to-underground transient electromagnetic method (SUTEM). We first analyze the differences between the surface TEM and SUTEM with a uniform half-space model. Secondly, we establish a geophysical model for water-bearing goafs and simulate the response signals at different depths with a vector finite-element method. Finally, we conduct a field experiment of SUTEM. The results of the simulation and experiment show: 1) When the surveying line is below the water-bearing goaf, the abnormal response information is mainly focused on the ascending segment of the electromotive force (EMF) curve, and the relative difference (RD) increases with the value of h/z decrease; 2) Appling SUTEM, we can accurately map the lateral position of the water-bearing goaf with the RD.
Characterization of Geological Structures under Thick Quaternary Formations with CSAMT Method in Taiyuan City, Northern China
Authors: Yu Chuantao , Chang Suoliang , Han Yu , Liu Jishan , Li Enguo
Published: December 2020

A controlled-source audio-frequency magnetotelluric (CSAMT) survey was used to detect geological structures beneath the thick quaternary formation in Taiyuan, Shanxi Province, northern China. Two main CSAMT survey lines with 182 survey sites were recorded. A two-dimensional (2D) inversion technique was used to interpret the CSAMT data. The inversion results suggested that: 1) there are four main buried faults named F1, F2, F3, and F4 with dip angles about 65° across the survey line from west to east, the fault displacements of these faults are about 230 m, 180 m, 220 m and 200 m, respectively; 2) the depth of the bedrocks decrease from 1600 to 500 m along the survey lines; and 3) from top to bottom, there are four major layers in the survey area that include the upper layer with the resistivity less than 40 ohm-m represents unconsolidated sediments in the Quaternary formation, a second layer with the resistivity range from 40 to 120 ohm-m represents mudstone and sandstone, a third layer with the resistivity range from 120 to 280 ohm-m represents coal measure strata in the Permian and Carboniferous and a bottom layer with the resistivity higher than 280 Ω·m represents limestone in Ordovician. The CSAMT method is an effective technique for exploring buried fault of several hundred meters deep in metropolitan environment.
Integrated Investigation for Geological Detection and Grouting Assessment: A Case Study in Qingdao Subway Tunnel, China
Authors: Guo Qian , Pang Yonghao , Liu Rentai , Liu Bin , Liu Zhengyu
Published: December 2020

Subway tunnel construction plays a significant role in the development of urban underground space. Advance surface grouting treatment of adverse subsurface geological bodies is an effective measure to avoid the accidents during subway construction. This paper describes the successful application of geological prospecting and grouting assessment at the tunnel site of Qingdao subway line No. 1. The study area is located in a coastal bedrock fissure water distribution area. It was decided to conduct surface grouting to reduce the high risk of water inrush. Integrated investigation consisting of electrical resistivity tomography (ERT), seismic ahead prospecting, surface vertical drilling and cross-hole ERT was conducted to ascertain the geological conditions and guide the grouting scheme design. Surface ERT and seismic ahead prospecting were adopted to provide a rough survey of water bearing conditions and fractured zones. Then, detailed imaging was conducted using cross-hole ERT inversion with the inequality constraint based on the information obtained using surface vertical drilling. The shape and location of three water bearing structures were identified. Based on the integrated investigation results, an appropriate grouting scheme was designed. After the application of grouting, cross-hole ERT was carried out again to assess the effect of grouting by comparing the vibration of twice inversion results of cross-hole ERT and resistivity tests of the grout sample. Such information serves as a basis for guiding geotechnical excavations in complex urban environments and avoids the risk of construction accidents.