Time Domain Electromagnetic Soundings Research Articles

Integration of Geophysical and Hydrochemical Methods to Determine the Groundwater Contamination in Al-Hosayniat Landfill South East Mafraq City, Jordan

An integration of Geophysical – Electromagnetic and hydro-chemical methods was used to investigate the potential of groundwater contamination due to Al-Hosayniat Municipal Landfill (HL) southeast of Mafraq city. Twenty-five Time Domain Electromagnetic (TDEM) soundings were carried out inside and outside the HL in addition to one WNW-ESE Very Low Frequency (VLF) profile. The TDEM's results help to define the subsurface geology and structures down to 240m depth. The results also depict the presence of a major fault striking NW-SE that crosses the whole landfill, this fault is documented in the surface geological map, and it was delineated and imaged by TDEM measurements and detected at larger depths. VLF results also detected the presence of a major fault beneath the landfill. The presence of the fault just beneath the HL may enhance the leachate movement which can imply groundwater contamination hazards for a longer period as it is a preferential pathway for contaminants. The results of water quality analyses of adjacent wells show higher concentrations of Na+, SO-24, TDS in some wells and this can be ascribed to agricultural activities and over-pumping in the area rather than landfill leachate. The heavy metal concentrations were found to be within the permissible limits and did't indicate direct contamination due to the HL. However, Fluorite (F-) shows a high concentration of (1.3mg/l) in WS4 and WS5 wells and approaches the permissible limit (1.5mg/l) according to the Jordan Water Standards (JWS). Bromide (Br) shows high concentration of (0.6mg/l) in well Al-2462.

Shallow Subsurface Structure of the Moon: Key Questions for Future Exploration

Lunar shallow subsurface structure is important in revealing the formation and evolution of the Moon. Therefore, a review of key issues in the lunar shallow subsurface structure will help deepen our understanding of the Moon. From a global perspective, lunar shallow subsurface structure is formed by endogenic and exogenic geological processes such as volcanic activities, tectonic activities, meteorite impacts, and space weathering. Its morphological characteristics and stratigraphic structure record the evolution of these geological processes. Recent lunar exploration missions have returned new samples and high-resolution data that have greatly enriched our knowledge. On the basis of reviewing the research progress of radar detection, crater-based excavation analysis, material inversion, and heat flow measurement, we also discuss the processes that contribute to the formation of the lunar shallow surface structure, such as volcanoes, impacts, tectonics, and space weathering. The main hot issues were sorted out and focused on 3 areas: transformation of lunar shallow subsurface structure by geological processes, environment and material composition of the lunar shallow surface structure, and physical properties of lunar shallow surface structure. Overall, existing research on the lunar subsurface has made significant progress, but it has also brought more new unsolved mysteries. It is necessary to introduce new applied payloads such as synthetic aperture radar (SAR), orbiter subsurface investigation radar (OSIR), or time-domain electromagnetic sounding (TDEM) to provide higher-resolution subsurface data, and develop better interpretation methodologies, to further deepen the understanding of the lunar shallow subsurface structure and indeed reveal the mechanism of lunar geological evolution.

Groundwater potentiality mapping: A case study in Baba and Sidri watersheds, South Sinai, Egypt

Groundwater potential zone (GWPZ) mapping is a multi-parameters approach that can assess the groundwater potentiality in mountainous terrain and coastal areas. This approach utilizes the geomorphology, lithology, rainfall, structure lineaments density, drainage density and slope which are the major effective factors controlling the groundwater potentiality. Primarily, these factors are prepared in the form of thematic layers using GIS technique, and then assigned different weights for these thematic layers using Analytical Hierarchy Process (AHP) technique to explore the GWPZ. This GWPZ is generated by the linear weighted sequence of all the prepared thematic layers. The moderate GWPZ (41.8%) sites are located in the main Wadi channels and alluvial fan at western portion; whereas, the high GWPZ (29.8%) concentrates in Homaier depression at the eastern region. Vertical electrical soundings (VES) and time-domain electromagnetic soundings (TEM) measurements have been achieved at high GWPZ to estimate depth and thickness of both saturated and unsaturated areas with water. This geophysical investigation has been done to confirm and support the effectiveness of applied factors of GWPZ mapping. The findings of these measurements are validated by standardizing the measured electrical resistivity values with the sequential layering layout and data records for five wells drilled at the locations of the geophysical soundings. VES and TEM data show the existence of moderately thick adjacent aquifers, covered with a dry area of different thicknesses (18–50 m). The aquifer units with thickness ranging from 43 to 71 m has resistivity values of 22–50 Ω m which is an indicator of freshwater content.

Set of Engineering and Geophysical Methods for Determining the Volume of Homogeneous Industrial Waste at Sites of Accumulated Environmental Harm

The paper presents the application results of geophysical methods (micro-near-field time-domain electromagnetic sounding and ground penetrating radar profiling) performed in 2022 to determine the volume of homogeneous industrial waste in collection ponds using the example of the phenol lake within the city limits of Ulan-Ude , The Republic of Buryatia. The boundaries and volumes of industrial waste disposal were determined, and the position of the overlying and bottom beds of the phenol pound were recorded. The migration channel of hydrophilic chemical pollutants from the bed of the studied object was identified and the reservoir was installed to collect, over the years of infiltration processes, fluid saturated with hydrophilic chemical pollutants from the phenol pound. 3D models of the industrial waste deposits in the phenol lake and 3D models of the identified collector were built. It was concluded that the used set of geophysical methods was effective for solving similar engineering, environmental and geoecological problems.

Groundwater quality assessment along the West of New Damietta Coastal City of Egypt using an integrated geophysical and hydrochemical approaches

Recently, the groundwater became very important source for the Egyptian water balance. Therefore, assessing its quality and quantity is necessary before initiating any developmental plans using this resource. In this research, a new operated power plant, which is located in the coastal area of West New Damietta City, north-east of Egypt was designed to work using the coastal groundwater aquifer. Therefore, an integrated approaches of both geophysical methods and hydrochemical analysis were applied to identify the subsurface lithology, the water-bearing layers and determine the potential use of such coastal groundwater. Therefore, a total of seventeen vertical electrical soundings (VES) and five time-domain electromagnetic soundings (TEM) were performed. Moreover, groundwater samples were collected from seven existing wells to be analyzed for water quality assessment. The geophysical results identified five geoelectric layers. The first geoelectric layer has a resistivity of 1–7.9 Ω m and a thickness range of 7–9 m. The second layer has a resistivity of 0.9–4.4 Ω m and a thickness range of 7–8 m. The third layer is 10–21 m thick with a resistivity value of 0.5–2 Ω m. The fourth layer, which is thicker (29 to 42 m), has a resistivity of 0.7–3 Ω m, while the last layer has a resistivity of 1.7–9 Ω m. According to the hydrochemical analysis, the aquifer is dominated by Na–Cl water type. The brackish nature of the water is revealed by the TDS range of 7035 mg/l to 7735 mg/l. The results collected demonstrate the groundwater's quantity and quality availability for the power plant’s sustainable use.

Changes in aquifer properties along a seasonal river channel of the Niger Basin: Identifying groundwater recharge pathways in a dryland environment

In drylands of tropical Africa, groundwater plays a fundamental role in alleviating food insecurity and adapting to the effects of climate change. Substantial uncertainty persists in the renewability of groundwater resources in drylands and recharge pathways through the surface geology. Here we characterize the architecture and hydrogeological properties of alluvium and underlying sandstone and crystalline basement rocks along the ephemeral River Goulbi de Maradi in the Iullemmeden Basin of Niger using Magnetic Resonance Soundings (MRS), Time-Domain Electromagnetic (TDEM) soundings, and borehole lithological data. Considerable variations in lithological facies and hydrophysical properties are found along a series of 5 transects perpendicular to the seasonal/ephemeral river channel and adjacent plateaux of the Continental Hamadien (CH) sandstone. The CH aquifer comprises a pebbly sand facies upstream and sandstone clay facies downstream with Farak-type sandstones located at the base of the two facies. Consistent with these variations in facies, the geophysical parameters decrease from 19%, 390 ms, and 800 Ω m upstream to 3%, 160 ms, and 10 Ω m downstream, respectively for effective porosity, relaxation time, and resistivity. The transmissivity and specific yield estimated from the decline of MRS longitudinally also vary from upstream to downstream. The combined use of surface geophysics constrained by lithological borehole logs provides vital insight into groundwater replenishment in this dryland environment.

Hydrogeophysical characterization of the Southern Red Sea coastal aquifer, Saudi Arabia, using Time-Domain electromagnetic method

The research aims to characterize the shallow coastal aquifer of the Red Sea in terms of lateral and vertical extensions and to determine the factors controlling the quality of groundwater using the Time-Domain Electromagnetic sounding method. The aquifer consists of alluvial sediments with an increasing thickness toward NE. Groundwater resistivity is variable from less than 5 Ω.m at the coastal strip to 20 Ω.m at 5 km toward NE. Furthermore, resistivity reached up to 100 Ω.m in other parts of the area. Variations in aquifer resistivity are attributed to lithological changes and seawater intrusion. Aquifer resistivity and the total dissolved solid values from wells indicate that the aquifer is adequate for agricultural usage except along the coastal areas.

The first experience of studying the folded structure of coal seams by seismic exploration in the Gorlovsky anthracite basin

The results of experimental and methodological seismic and electrical exploration of near-field time-domain electromagnetic sounding (NFTDES) along the profile crossing the productive formation of сoal seams in the Gorlovsky anthracite basin (Doroginskoye deposit, Shadrinsky block) are presented. The possibility of studying coal-bearing series at depths up to 300-350 m is noted. The obtained CDP time cross sections indicate the possibility of displaying some elements of the structure of thick anthracite seams in the wave field, that allowing for reconstruction of their folded features. Using the first arrivals of longitudinal waves (at distances up to 800 m), seismic tomography allows scientists to reconstruct in detail the velocity structure of the near-surface part of the section to depths of 120-150 m and to identify low-velocity local objects corresponding to the upper edges of the thickest coal members in the weathering crust and in the upper part of Permian deposits. The resolution of velocity profile decreases at a given length of the traveltime graph with a further increase in depth to 300 m.

Three-Dimensional Magnetotelluric Characterization of the Travale Geothermal Field (Italy)

The geoelectrical features of the Travale geothermal field (Italy), one of the most productive geothermal fields in the world, have been investigated by means of three-dimensional (3D) magnetotelluric (MT) data inversion. This study presents the first resistivity model of the Travale geothermal field derived from derivative-based 3D MT inversion. We analyzed MT data that have been acquired in Travale over the past decades in order to determine its geoelectrical dimensionality, directionality, and phase tensor properties. We selected data from 51 MT sites for 3D inversion. We carried out a number of 3D MT inversion tests by changing the type of data to be inverted, the inclusion of static-shift correction at some sites where new time-domain electromagnetic soundings (TDEM) were acquired, the grid rotation, as well as the starting model in order to assess the connection between the inversion model and the geology. The final 3D model herein presents deep elongated resistive bodies between the depths of 1.5 and 8 km. They are transverse to the Apennine structures and suggest a correlation with the strike-slip tectonics. Comparison with a seismic velocity model and well log data suggests a highly-fractured volume of rocks with vapor-dominated circulation. The outcome of this study provides new insights into the complex geothermal system of Travale.

Geophysics and remote sensing applications for groundwater exploration in fractured basement: A case study from Abha area, Saudi Arabia

Groundwater can be the only salvation in arid or semi-arid mountainous areas, especially for those covered by basement rocks. The fractured groundwater aquifers are characterized by a lack of extension in all directions and the distribution of the main fractured and shear zones. An integrated approach of satellite remote sensing and geophysical techniques was used to investigate groundwater occurrence in the fractured aquifers of the mountainous area north of Abha city. A digital elevation model (DEM) was used to extract the streamlines and determine the eastward direction of the surface water flow. The average annual precipitation over the study area shows a positive increase trend estimated at 156 mm yr-1 based on Tropical rainfall measuring mission (TRMM) data during the 2002–2018 period. Seven vertical electrical soundings (VES) using Schlumberger array and twelve time-domain electromagnetic soundings (TEM) using an induction loop with size 50 by 50 m were conducted to detect accumulated groundwater in irregular shape pockets within the fractured basement rocks of the area. VES's and TEM indicate the occurrence of water saturation zones at depths varying from 45 to 60 m. The thickness of the saturated zone exceeds 100 m in some parts, extending toward the northeast-southwest direction parallel to the fractures and faults. The integrated approach provides a reliable study to better understand the groundwater occurrence in fractured basement aquifers.

Электромагнитные исследования на территории Алтае-Саянской горной области

A new software-measuring complex has been developed for recording non-stationary electromagnetic soundings based on mobile modules created on the basis of 24-bit ADCs, with built-in GPS receivers, with recorders located directly at the field sensors, arithmetic sampling step and recording of all signal realizations. The deep structure of the Uimon depression in Gorny Altai has been studied based on the time-domain electromagnetic sounding. Research is relevant due to the high seismic hazard of the area, and is also in demand for prospecting and exploration of predicted minerals here. To construct geoelectric models, data from several years of measurements were used, during which more than 60 soundings were performed. At this stage, the interpretation was performed using computer systems within the framework of a horizontally layered model. The interpretation results are presented in the form of sections and threedimensional visualizations, which clearly reflect the structure of the depression. Further, three-dimensional modeling and additional measurements are planned to verify and refine the results obtained.

Application of Time Domain Electromagnetic survey to detect fractured limestone aquifer in desert fringes, West Assiut, Egypt

ABSTRACT New agriculture projects in the desert fringes along the western side of the Nile Valley of Egypt need exploring new groundwater resources. Time Domain Electromagnetic (TDEM) technique was used to acquire the field data. This technique is focusing on two main objectives. The first objective is to test the availability of applying TDEM in areas where other DC resistivity methods can’t be applied due to the presence of a high resistive layer on the ground surface such as in the investigated area. The second objective is detecting the geoelectrical succession, emphasising on the water-bearing layer, which is represented by the fractured Eocene limestone layers. Results obtained from TDEM soundings were represented in the forms of cross sections and maps to illustrate the aerial distribution of the different geoelectrical layers and pay attention on the water-bearing layer. These results show up a good agreement with the data obtained from the drilled wells in the study areas. Accordingly, TDEM method is a suitable choice when other DC resistivity tools were failed to acquire field data. Moreover, this technique helped to determine the parameters of the water-bearing layer such as resistivity, thickness, and extension. Also, it gives an idea about the hydrogeological setting of the study area where the water-bearing the fractured limestone layer overlays the low resistivity shale beds. New sites were recommended to drill productive wells in the western and southern parts of the study area based on the resistivity values and the thicknesses of the water-bearing layer.

Integrated electromagnetic survey for groundwater exploration: case study at El-Minya, western desert of Egypt

ABSTRACT The determination of groundwater potentiality is one of the most significant challenges in hydro-geophysical research, especially in arid areas with limited water resources. A geophysical survey was carried out in the northwest of El-Minya Governorate to investigate the groundwater aquifer. A total of 20 controlled source audio-magnetotelluric (CSAMT) and 20 time domain electromagnetic soundings (TEM) were surveyed along two parallel profiles with station spacing varying between 500 and 2000 m. The CSAMT data was acquired using a hybrid source of low frequency band (0.1 Hz – 1 KHz) and standard high frequency band (10 Hz- 100 KHz). For the TEM survey, a coincident loop of side length of 50 m was used. The results of the integrated interpretation of both data sets (TEM and CSAMT) show a good consistency in the conductivity distribution. However, inspection of the results of the cross section indicates that two to three geoelectrical layers can be recognised in the subsurface medium. The area’s water potentiality is divided into two levels: the first begins immediately beneath the rock cap at depths of over 50 m and reaches nearly 200 m in some spots. The second level begins at a depth of 250 m and continues to a depth of 500 m.

ГЛУБИННОЕ СТРОЕНИЕ РАЗЛОМНОЙ ЗОНЫ НА УЧАСТКЕ МУХОР-ТАРХАТА ЧУЙСКОЙ ВПАДИНЫ ПО ДАННЫМ НЕСТАЦИОНАРНЫХ ЭЛЕКТРОМАГНИТНЫХ ЗОНДИРОВАНИЙ С ИСПОЛЬЗОВАНИЕМ ТРЕХМЕРНОГО МОДЕЛИРОВАНИЯ

The paper presents the results of three-dimensional modeling of the fault structure in the central part of the Chuya depression in Gornyi Altai within the Mukhor-Tarkhata plot. On this site, from 2004 to the present, researchers of the IPGG SB RAS have been conducting regular annual observations by the method of nearfield time-domain electromagnetic sounding (TSB) to observe the process of restoration of the geological environment after the catastrophic Chuya earthquake with a magnitude of 7.3 in 2003. One of the aftereffects of the destructive earthquake is fracture zones expressed on the surface. Numerous deformations of the surface and industrial objects are observed in the area of the Mukhor-Tarkhata village. The fault zone with sub-vertical fracturing, identified at the site by geological and electromagnetic data, was activated after the earthquake. Detailed data on the geoelectric structure are required for the interpretation and analysis of monitoring data. Based on the interpretation of the near-field time-domain electromagnetic sounding data, the deep structure of the fault zone was obtained. To verify and clarify structural features of the geoelectric model, three-dimensional modeling was performed.

СНИИГГИМС – ИНИЦИАТОР ПОСТАНОВКИ НЕФТЕПОИСКОВЫХ ЭЛЕКТРОРАЗВЕДОЧНЫХ РАБОТ ЗСБ НА СИБИРСКОЙ ПЛАТФОРМЕ (ИСТОРИЧЕСКИЙ ЭКСКУРС)

The article is devoted to the origin history and development of electric exploration of NFTDES (near-field time-domain electromagnetic sounding) in Siberia. The described historical insight covers the period from the mid-sixties to the mid-nineties of the last century – the period of origin, flourishing and extinction (thank God, temporary), associated with the well-known “reconstruction of our lives”. The main attention is paid to the description of events that took place within the framework of the oil exploration direction, in the midst of which the author was lucky enough to work all this time. Using the traditional terminology of 2020, this was the beginning of the “first wave” of formation and development of the Siberian school of electric exploration, the core of which was the “tandem” of electric explorers of SNIIGGiMS and IGiG SB AS USSR.

The Global Search for Liquid Water on Mars from Orbit: Current and Future Perspectives.

Due to its significance in astrobiology, assessing the amount and state of liquid water present on Mars today has become one of the drivers of its exploration. Subglacial water was identified by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) aboard the European Space Agency spacecraft Mars Express through the analysis of echoes, coming from a depth of about 1.5 km, which were stronger than surface echoes. The cause of this anomalous characteristic is the high relative permittivity of water-bearing materials, resulting in a high reflection coefficient. A determining factor in the occurrence of such strong echoes is the low attenuation of the MARSIS radar pulse in cold water ice, the main constituent of the Martian polar caps. The present analysis clarifies that the conditions causing exceptionally strong subsurface echoes occur solely in the Martian polar caps, and that the detection of subsurface water under a predominantly rocky surface layer using radar sounding will require thorough electromagnetic modeling, complicated by the lack of knowledge of many subsurface physical parameters. Higher-frequency radar sounders such as SHARAD cannot penetrate deep enough to detect basal echoes over the thickest part of the polar caps. Alternative methods such as rover-borne Ground Penetrating Radar and time-domain electromagnetic sounding are not capable of providing global coverage. MARSIS observations over the Martian polar caps have been limited by the need to downlink data before on-board processing, but their number will increase in coming years. The Chinese mission to Mars that is to be launched in 2020, Tianwen-1, will carry a subsurface sounding radar operating at frequencies that are close to those of MARSIS, and the expected signal-to-noise ratio of subsurface detection will likely be sufficient for identifying anomalously bright subsurface reflectors. The search for subsurface water through radar sounding is thus far from being concluded.

Geophysical and hydrogeochemical investigations of Nubian sandstone aquifer, South East Sinai, Egypt: Evaluation of groundwater distribution and quality in arid region

The expansion in human activities, the absence of running water in South Sinai province in northeastern Egypt and the high cost of seawater desalination render groundwater the essential source for potable water in this arid region. This contribution represents the integration of geophysical and hydrochemical investigations to delineate groundwater distribution and evaluate the water quality of the Cretaceous sandstone aquifer of Wadi Barqa area, Southeastern Sinai. The locations of sites, suitable for geophysical sounding measurements, were selected using digital elevation map. Vertical electrical sounding (VES) and time-domain electromagnetic sounding (TEM) measurements were carried out to determine the depth and thickness of the unsaturated and water-saturated zones as well as the groundwater quality, which were verified by calibrating the estimated electrical resistivity values with the design and logs data of eleven drilled wells next to the sites of geophysical soundings. The VES and TEM data revealed the presence of relatively thick zoned aquifer, overlain by unsaturated zone with variable thickness (83-65 m). The upper aquifer zone (25–43 m thick) is characterized by higher resistivity values (16–163 Ohm.m), reflecting fresh water signature, whereas the lower aquifer zone (122–150 m thick) has lower resistivity values (16–24 Ohm.m), indicating saturation with semi-fresh to relatively brackish water. Water samples, collected from wells taping the Nubian Sandstone aquifer, have average total dissolved solids (TDS) value of 544 mg/l. The hydrochemical parameters of these samples are consistent with NaCl water type with the majority of samples belonging to high salinity with low sodium categories. This suggests that the groundwater of the aquifer was dominated by old meteoric origin. The compositional characteristics of the groundwater of the investigated aquifer indicate suitability for domestic and irrigation purposes. However, due to the arid nature of Southeastern Sinai province, it is recommended to use this groundwater as potable water.

Mapping sea water intrusion in coastal area using time-domain electromagnetic method with different loop dimensions

Time Domain Electromagnetic (TDEM) method has been widely used in mapping and assessment of groundwater resources and sea water intrusion along coastal alluvial plains. TDEM soundings were used to define aquifer zones in the alluvial aquifer at Al Khoud coastal area in North Oman. The main aquifer zones, composed of clean gravels, clayey gravels, and cemented gravels, could be identified, along with the basal contact of the aquifer. The TDEM data were also used to map the depth to the interface between freshwater and saline-water along the coast. The inland extents and thickness of the saline water intrusion zone were mapped along two sets of TDEM profiles. The depth to the intrusion zone was investigated using different transmitter loop sizes. Quality assurance of the data was done by comparing the resistivity distribution derived from TDEM with the electrical conductivity and resistivity logs from available well logging data in the study area. TDEM proved to be a successful tool for mapping saline zones and fresh water in arid environment with high depth of penetration and speed of field operation.

Utilizing the Geophysical and Hydrogeological Data for the Assessment of the Groundwater Occurrences in Gallaba Plain, Western Desert, Egypt

The investigated region is located in the western desert fringes of the Nile Valley which requires studies of groundwater related to the many projects of land reclamation. The key objective of this paper is to estimate the qualitative and geometrical features of the investigated aquifer. Using 60 vertical electrical sounding and time-domain electromagnetic soundings allows us to suggest one possible model of the geometrical features of the local aquifer. A hydrogeological monitoring has been undertaken to investigate the current groundwater situation at the Gallaba plain. Such hydrological monitoring has not been undertaken before in detail. The results show that the investigated region has high groundwater potentialities in two main aquifers which belong to Pleistocene: shallow fresh water and deep brackish water. The lithological and structural elements contribute mainly to recharge and store the groundwater in the western part of the River Nile in Kom Ombo graben. The geochemical properties of the groundwater of the studied aquifers reflect meteoric water, which is a fresh to slightly brackish water. The small amount of groundwater salinity arises from silicate weathering and evaporation processes occurring in the aquifer matrix. Moreover, most of the studied groundwater samples are unfit for human consumption. Such samples are very satisfactory for livestock and poultry purposes and they can be used for irrigation using modern and improved irrigation methods e.g. sprinkler and drip methods. Furthermore, the hydrogeological monitoring of the concerned area indicates that it has high groundwater potentialities which will support its sustainable development.

Geometry and Structure of a Fault‐Bounded Extensional Basin by Integrating Geophysical Surveys and Seismic Anisotropy Across the 30 October 2016 Mw 6.5 Earthquake Fault (Central Italy): The Pian Grande di Castelluccio Basin

AbstractThe Pian Grande di Castelluccio (PGC) basin is the main Quaternary depocenter of the Mt. Vettore‐Mt. Bove normal fault system (VBFS), responsible for the 30 October 2016 Mw 6.5 Norcia earthquake (central Italy). Coseismic surface faulting through the basin attests the occurrence of active splays of the seismogenic master fault; thus, we explore the subsurface basin structure to infer the long‐term behavior of the VBFS. We integrate electrical resistivity tomography (ERT), time domain electromagnetic soundings (TDEM), and horizontal‐to‐vertical spectral ratios of ambient seismic vibrations (HVSR) along a transect crossing the surface ruptures. The ERT models provide high‐resolution details of three shallow fault zones. One‐dimensional resistivity models from TDEM and HVSR frequency peaks suggest abrupt steps in the top bedrock caused by previously unknown faults and indicate an infill thickness of up to ~300 m. We also analyze shear wave splitting of S phases (fast direction φ and delay time δt) from local earthquakes recorded during our surveys to better constrain the fracture field and the properties of the inferred fault zones. We relate the retrieved pattern of fault‐parallel φ, and the associated larger δt, to the main and secondary faults in the upper crust and to the cracks or shear fabric in the damage zones of the active splays. The PGC basin is due to the interference of an older N30° striking fault system subsequently crosscut by the N150° striking VBFS, which is currently active, seismogenic, and capable of rupturing the surface during M > 6 earthquakes.