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Research has been conducted using the gravity method in the Wai Selabung area, South Ogan Kemiring Ulu Regency, South Sumatra Province, correlated with geological data, magnetotellurics, and geochemical data. This research aims to get structural patterns, subsurface models and identify the heat source and reservoir areas of the Wai Selabung geothermal system. This study uses the gravity method to model the subsurface, which is correlated with magnetotelluric and geochemical data to identify reservoir prospect areas. The results obtained from this research include residual anomalies in the research area showing the presence of a northwest-southeast trending fault structure by the main fault structure of this area trending northwest-southeast and slightly southwest-northeast. Analysis of the Second Vertical Derivative value of zero indicates the boundaries of the geothermal reservoir in the middle of the research area. The results of the 3D inversion modeling of the research area show that low density (2 to 2.15 g/cm3) indicates the location of the reservoir, medium-density values (2.2 to 2.4 g/cm3) are tertiary sandstone sedimentary. The high-density distribution value (2.5 to 2.9 g/cm3) indicates a potential heat source. And based on the analysis of the gravity method correlated with geological data, magnetotelluric, and geochemical data, the prospect area for the Wai Selabung geothermal reservoir, is around Teluk Agung, Perekan, and Talang Tebat.

In this study, the X5 KCC in Shiquan Coal Mine was investigated by means of controlled source audio magnetotelluric exploration and borehole television. In this way, the subsection geological structure of the KCC was obtained. Next, the geological and electrical characteristics of each part were analyzed, and it is concluded that the development status of the mud part under coal seam floor is the key part to judging whether water inrush will occur during working face recovery under aquifer pressure. Furthermore, the mineral compositions of purplish-red mudstone and lime mudstone were obtained by performing an X-ray diffraction experiment on the KCC interstitial materials. On this basis, the water insulation properties of the mud part were qualitatively evaluated. Finally, the tensile strength of the mud part was obtained by the Brazilian splitting method, and the water insulation ability of the mud part at the periods when the tunneling roadway and the working face passed the KCC was calculated, respectively. The research results boast guiding significance for safe recovery of the working face passing KCCs under aquifer pressure.

SUMMARYMagnetotelluric (MT) observations have revealed subvertical electrical conductors that extend from shallow depths into the mid-crust at various geothermal zones, active volcanoes and active faults worldwide. These deeply rooted subvertical conductors have typically been interpreted to represent entire zones of dedicated fluid transport through the crust. We estimate the high-resolution 3-D crustal resistivity structure below the Kuju Volcanoes, Japan, using dense observations from 153 broad-band MT measurement sites and 40 telluric measurement sites. The resistivity structure highlights subvertical conductors that merge into a deep conductor to the north of the volcanoes, with deep low-frequency earthquakes occurring near the southeastern edge of this subvertical conductor at 10–30 km depth. This deep conductor branches into several subvertical conductors at 2–10 km depth, coinciding with a shallow zone where tectonic earthquakes rarely occur. The surface expressions of active geothermal areas and past volcanic eruptions are all located above the edges of the conductors at 2–6 km depth. Widespread conductive layers exist around the volcanoes above 2 km depth, and their distribution approximately corresponds to a low-gravity-anomaly zone. We discuss the nature of these subvertical conductors, the potential causes of their complex structure and their relationship to local magmatic fluid transport. These subvertical conductors, a shallow clay-rich layer, developed fracture systems and high-strength solidified magma may all contribute to magmatic fluid transport to the surface at the Kuju Volcanoes. In this study, we add the possibility that the edges of these subvertical conductors act as important magmatic fluid pathways.

A new permanent geophysical station was installed in the Seymour-Marambio Island, Antarctica, for monitoring electromagnetic, CO2, and CH4 gas signals. Those signals require specialized low noise instruments and the survey shall be carried out in places far away from cultural noise, such as populated human settlements. The most suitable place would be near the Earth's poles, where noise is the lowest possible. To measure these variables, the Geophysical Instrumentation Laboratory (Laboratorio de Instrumentación Geofísica - LIG) of the Universidad Nacional de Colombia, in a partnership with the Instituto Antártico Argentino (IAA) under the Argentinean National Antarctic Direction (Dirección Nacional del Antártico - DNA), deployed the COCOAonMEAT project, oriented to design, built and install a low-cost station with time synchronization via GPS and data transmission in almost real-time. Since January 2020, the project monitors continuously (24/7) seven variables: three magnetic components, two electric dipoles, methane (CH4), and carbon dioxide (CO2) gas. Due to operative facilities and its low electromagnetic noise, the place chosen for its installation was the Argentinean Marambio Scientific Base in the Antarctic Peninsula, with the Multidisciplinary Antarctic Laboratory's collaboration (Laboratorio Multidisciplinario Antártico en la Base Marambio - LAMBI). This station provides valuable information on electromagnetic signals and greenhouse gases related to regional tectonic activity and local perturbations associated with global climate change.

The North China Craton is the oldest continental block, and has suffered from large-scale lithospheric thinning and destruction, which in turn led to gold deposits in northern China. The decratonic gold deposits in the North China Craton became the most important gold deposits in China, and geophysical methods are key means to detect and discover gold deposits there. In this paper, based on the geological and petrophysical characteristics of the North China Craton, the geological model of the decratonic gold deposits is transformed into a geophysical model. At present, two methods of geophysical exploration of decratonic gold deposits are in use: rapid and efficient exploration on the scale of the ore concentration area, and large depth exploration on the scale of the deposit area. In detail, the airborne electromagnetic, magnetic and gravity methods are used to detect the shallow (1,500 m) anomaly area on the scale of the ore concentration area. Through the ground-controlled source electromagnetic and ground magnetotelluric methods, explorations for targets at significant depth (5,000 m) are carried out in the mining area. Then, taking the Liaodong ore concentration area as an example, geophysical methods are used to discover two prospecting areas around the Jianshanzi Fault in the Qingchengzi ore concentration area, Baiyun-Xiaotongjiapuzi deep prospecting area, and Qingchengzi deep prospecting area. Next, three prospecting areas are delineated around the Jixingou Fault in the Wulong mining area, Wulong deep prospecting area, Weishagou deep prospecting area, and Chang’an deep prospecting area. The anomalies in the ore concentration area and mining area are revealed by means of three-dimensional exploration methods, thereby providing technical support for the exploration of metal minerals such as decratonic gold deposits.

Geophysics offers an important means to investigate the physical processes occurring inside the earth. In particular, since the 1960s, electromagnetic (EM) methods have played important roles in mineral exploration and engineering investigation. Such investigation requires extensive data acquisition and experimental analysis based on geophysical techniques. However, high-performance geophysical equipment, particularly EM exploration equipment, has been dominated by large geophysical companies from the United States, Canada, Germany, and other European countries for decades. This has limited the development of deep exploration technology in China. Recently, we have developed a high-resolution acquisition system with a wireless control unit and a high-power transmitting system for surface EM prospecting (SEP). The new system has been tested in the high-intensity, noisy environment in Jian-sanjiang area, Heilongjiang Province. We then conducted a field survey on the western edge of Qaidam Basin, Qinghai Province. A highly conductive anomaly was found in the upper mantle below the Qinmantage Mountains, which indicates a possible northward fluid channel that runs from below the Qinmantage Mountains to the bottom of the western crust of the Qaidam Basin. Identification of this significant feature was made possible by the new SEP for its better resolution than the previous systems. Also, geophysical analysis confirmed that the thick Cenozoic sediments of the Qaidam Basin are underlain by rigid Precambrian basement rocks and are characterized by a series of folds. The resistivity profile indicates that the Qaidam Basin was formed due to the folding structures in the northern part of the Qinghai-Tibet Plateau which provided an additional evidence for the uplifting of the Qinghai-Tibet Plateau.

The Yinchuan Graben (YG) is situated in the transitional area between the Tibetan Plateau, Ordos Block (OB) and Alxa Block (AB). The dynamic mechanism of the YG is controversial because of its unique tectonic environment. This study used a broadband magnetotelluric profile constrained by high-density point spacing to reliably obtain the deep electrical structure across the Helanshan Orogenic Belt and YG and to discuss the dynamic mechanism of the YG. The main research results are as follows. 1) Our profile and previous seismic profiles show a low-resistivity and low-velocity body in the deep YG, which extends upward and cuts through the bottom boundary of the upper crust, and all results indicate that this body may be the result of partial melting due to upwelling mantle material. 2) Our profile also shows a high-resistivity anomaly in the middle-lower crust of the Helanshan orogenic belt, which can be interpreted as intrusive rocks formed by the emplacement of partially melted materials. 3) The Helanshan east piedmont fault dips eastward and intersects with the Yellow River fault at the depth of 20 km, and the typical structure of the intersection may be the seismogenic structure of the Pingluo Ms8.0 earthquake. 4) The evolution of the YG may have been controlled by various dynamic mechanisms, and the initial formation of the YG may have resulted from the upwelling mantle material beneath the northern OB; the evolution of the YG since 10 Ma may also have been affected by lateral mantle flow from the Tibetan Plateau to the gap between the OB and AB.

An electrical resistivity model beneath Azumayama Volcano, NE Japan, is explored using magnetotelluric method to probe the magma/hydrothermal fluid distribution. Azumayama is one of the most concerning active volcanoes capable of producing a potential eruption triggered by the 2011 Tohoku-Oki Earthquake. The three-dimensional resistivity model reveals a conductive magma reservoir (

The Santa Lucia River Basin Trough is located in the southern sector of the Eastern Republic of Uruguay and has an area of almost 6,000 km2. In this work, the depth to the basement in the SW sector of the Santa Lucia Basin (SLB) was determined, using geophysical methods of exploration. The interest of exploring this geological basin is to determine its depth, recognizing the possible existence of deep aquifers, and the feasibility of hydrothermalism. For this reason were acquired, processed, inverted, and interpreted 10 magnetotelluric (MT) soundings. A 3D inversion based on the ModEM code was performed, and a 2D inversion (NLCG) of the invariant determinant along a profile that crosses the study area was carried out; their comparison yields similar resistivity and structural models results. The resistivity modeling was complemented with a Bouguer anomaly map created from a gravimetric database of 157 stations. Our geophysical results indicate that the Santa Lucia trough deepens toward the E-NE, reaching sedimentary thicknesses that may exceed 950 m. Outside the studied sector, its depth increases according to the gravity minimum, toward the NE of the area. Therefore, sandy or deep fractured episodes could harbor hot springs, whose temperature, considering the normal geothermal gradient of 30 °C/km, would approximately be in the range of 36–40 °C.

Zhongshan Station (69° 22′24.76 ′′s, 76°22′14.28′′E) is located in the Westoden Peninsula, Larsemann Hills area, Princess Elizabeth Islands, East Antarctica. Here, we report results from a magnetotelluric experiment and delineate the deep electrical conductivity structure beside the Zhongshan Station by using the data acquired during the 36th Chinese Antarctic Scientific Expedition. Magnetotelluric (MT) data have the advantages of wide range and large depth in geophysical surveying. Two-dimensional inversion of MT data was conducted using the nonlinear conjugate gradient algorithm, and the conductivity structure under the Larsemann Hills area was described. The simulation results show that the high resistivity level in the shallow layer represents the Quaternary glacial sediments on the surface of bedrock. Further, the underground electrical structure within the depth of 10 km in the middle section shows obvious horizontal difference and drastic longitudinal variation. The depth of 10–40 km is characterized by thick layer and low resistivity, the electrical structure is relatively uniform, and the low resistivity structure is geographically inclined slightly to the northeast. This section is characterized by low resistivity structure. The upper part of the southwest section is characterized by high resistance, and the middle and deep part (below 10 km) is characterized by relatively uniform and low resistance terranes. The discovery can be interpreted as follows: The low resistivity body in the southwest segment represents the core cratonic crustal structure of the southeast polar shield, while the low resistivity body with complex electrical structure in the middle 10 km depth of the section can be interpreted as the collision zone between the Prydz Orogenic Belt and the East Antarctic craton. Our study confirms the position of the Prydz Orogenic Belt under the Larsemann Hills of East Antarctica and depicts the electrical structure of the collisional amalgamation area, which provides evidence for further study of the splicing of the Gondwana archicontinent.

Newly, the Egyptian government initiated huge national projects for the reclamation and sustainable development of 1.5 million acres. Farafra Oasis is recognized as the focus of the first phase of this project where groundwater is the wellspring of the water for irrigation and drinking. Hence, exploration and assessment of groundwater aquifers are very essential in such area. A reconnaissance geophysical survey was conducted in the centre of Farafra oasis using Vertical Electric Sounding (VES), Transient electromagnetic (TEM), Audio-Magnetotelluric (AMT), Control-source Magnetotelluric (CSAMT), and Very Low Frequency (VLF) techniques for the investigation of shallow and deep groundwater reservoirs. In addition, geologic and stratigraphic information from the nearest well was utilized to confirm the geophysical outcomes. Integrated geophysical measurements succeeded to delineate the three zones A, B and C of the Nubian aquifer system in the investigated area. Also, several fault elements were delineated which control the influx and aggregating of the groundwater in both units; shallow and deeper one. Deeper aquifer (zone C) shows generally higher resistivity values, which consider the major aquifer of Nubian sandstone in the Western Desert of Egypt. Geochemical examinations of the groundwater sample show that the water is remarkable for all agriculture purposes (TDS = 95).

Large-scale electrical resistivity investigations of the Antarctic crust and upper mantle utilizing the magnetotelluric method (MT) are limited in number compared to temperate regions, but provide physical insights hard to achieve with other techniques. Key to the method's success are the instrumentation advances that allow microvolt (µV)-level measurements of the MT electric field in the face of mega-ohm (MΩ) contact resistances. Primarily in this chapter, we reanalyse existing data from three campaigns over the Antarctic interior using modern 3D non-linear inversion analysis, and offer additional geophysical conclusions and context beyond the original studies. A profile of MT soundings over the transitional Ellsworth–Whitmore block in central West Antarctica implies near-cratonic lithospheric geothermal conditions with interpreted graphite–sulfide horizons deformed along margins of high-grade silicate lithological blocks. Reanalysis of South Pole soundings confirms large-scale low resistivity spanning Moho depths that is consistent with limited seismic tomography and elevated crustal thermal regime inferences. Upper mantle under a presumed adiabatic thermal gradient below the Ross Ice Shelf near the central Transantarctic Mountains appears to be of a moderately hydrated state but not sufficient to induce melting. The degree of hydration there is comparable to that below the north-central Great Basin province of the western USA.

Earthquakes threaten people’s lives and property, especially when cities are affected. Thus, detecting the crustal structure and seismogenic background beneath cities is important if we are to lessen losses. Because the city of Zhumadian in Henan Province, China, is a well-developed area with a large population, more attention should be paid to earthquake detection. We therefore collected data from 15 magnetotelluric (MT) stations along a 55-km survey line across Zhumadian. Then, subsequent to acquisition, processing, and data inversion, we developed a preferred electrical resistivity model. We accurately relocated original earthquakes during the period between 1981 and 2019 within the study area using the double-difference earthquake location algorithm. The relocated earthquakes were projected onto our preferred MT model. The new resistivity model presented here reveals that saturated rocks, including rocks with porosities of 4.31–19.69% and moderate salinities of 10 g/L pore fluid and/or graphite, form conductive features in the upper crust. We also show that aqueous fluids derived from metamorphic dehydration within the lower crust and mantle, not melts, constitute mid-crustal conductors and facilitate detachment structures. The data show that the relocated earthquakes are located adjacent to the boundaries between conductive and resistive areas as well as at the bottom of fault fracture zones. These outcomes imply that the combination of rock failure and fault slipping triggers earthquakes.

The Great Sumatran Fault (GSF) activity is a severe threat to Banda Aceh development as the capital city of Aceh Province, Indonesia. The earthquakes originating along this fault trace, despite generating low strength, considerably threaten infrastructure and human lives. Therefore, a detailed study of the GSF activity and presence becomes critical. In this paper, we applied the Global Gravity Model plus (GGMPlus) to map the subsurface structure and modeling of two GSF segments with a resolution of 200 m/px, namely the Aceh and Seulimeum segments toward the north of the Sumatran Island. The Bouguer anomaly data are inconsistent with the geology of the study areas, dominated by igneous rocks on the Aceh segment and volcanic rocks on the Seulimeum segment. Further, the contrast between the Seulimeum segment in the northeast and the Aceh segment in the southwest can be demonstrated by high-pass filtering. The GGMPlus data validation results with field measurements using the Scintrex CG-5 Autograv, the root mean square error obtained via data comparison are 12.32% in the Krueng Raya fault zone, and 26.1% at the Seulawah Agam Volcano area, respectively. We also performed 2D gravity data modeling along with the Aceh and Seulimeum segments in the NW–SE direction. This model was then compared with the geological cross section, seismicity, and magnetotelluric data. The results of Singular Value Decomposition and Occam inversion show three vertical blocks of high densities with an interspersion of lower densities, which can be confirmed as the Aceh and Seulimeum segments. Based on data processing, it can be concluded that the GGMPlus satellite can improve the maps and images of the northernmost GSF structure.

In order to analyze the process of subduction of the Nazca and South American plates in the area of the Southern Andes, and its relationship with the tectonic and volcanic regime of the place, magnetotelluric measurements were made through a transversal profile of the Chilean continental margin. The data processing stage included the analysis of dimensional parameters, which as first results showed a three-dimensional environment for periods less than 1s and two-dimensional for periods greater than 10s. In addition, through the geomagnetic transfer function (tipper), the presence of structural electrical anisotropy was identified in the data. After the dimensional analysis, a deep electrical resistivity image was obtained by inverting a 2D and a 3D model. Surface conductive anomalies were obtained beneath the central depression related to the early dehydration of the slab and the serpentinization process of the mantle that coincides in location with a discontinuity in the electrical resistivity of a regional body that we identified as the Nazca plate. A shallow conductive body was located around the Calbuco volcano and was correlated with a magmatic chamber or reservoir which in turn appears to be connected to the Liquiñe Ofqui fault system and the Andean Transverse Fault system. In addition to the serpentinization process, when the oceanic crust reaches a depth of 80 - 100 km, the ascending fluids produced by the dehydration and phase changes of the minerals present in the oceanic plate produce basaltic melts in the wedge of the subcontinental mantle that give rise to an eclogitization process and this explains a large conductivity anomaly present beneath the main mountain range.

Kusatsu-Shirane volcano has been a particular study field for hydrothermal system and phreatic eruptions with plenty of thermal springs, fumaroles, and a crater lake of Yugama. On 23 January 2018, a phreatic eruption occurred at the Motoshirane cone of Kusatsu-Shirane, where no considerable volcanic activity had been reported in observational and historical records. To understand the eruption process of such a unique event, we examined observed seismic, tilt, and infrasound records. The onset of surface activity accompanied by infrasound signal was preceded by volcanic tremor and inflation of the volcano for 2 minutes. Tremor signals with a frequency of 5–20 Hz remarkably coincide with the rapid inflation. We apply an amplitude source location method to seismic signals in the 5–20 Hz band to estimate tremor source locations. Our analysis locates tremor sources at 1 km north of Motoshirane and at a depth of 0.5–1 km from the surface. Inferred source locations correspond a conductive layer of impermeable cap-rock estimated by magnetotelluric investigations, and an upper portion of the seismogenic region, suggesting hydrothermal activity hosted beneath the cap-rock. Examined seismic signals in the 5–20 Hz band are typically excited by volcano-tectonic events with faulting mechanism. Based on the above characteristics and background, we interpret that excitation of examined volcanic tremor reflects small shear fractures induced by sudden hydrothermal fluid injection to the cap-rock layer. The horizontal distance of 1 km between inferred tremor sources and Motoshirane implies lateral migration of the hydrothermal fluid, although we have not obtained direct evidence. Kusatsu-Shirane has a series of unrest at the Yugama lake since 2014. However, inferred tremor source locations do not overwrap active seismicity beneath Yugama. Therefore, our result suggests that the 2018 eruption was triggered by hydrothermal fluid injection through an independent pathway that has driven unrest activities at Yugama.

En este trabajo se investiga el sector sudeste de la fosa tectónica del río Santa Lucía, ubicada al sur de Uruguay, mediante el empleo de métodos geofísicos de exploración. En particular, gravimetría, sondeos magnetotelúricos y eléctricos (SEV y Tomografía eléctrica). El interés de explorar dicha fosa radica en determinar su geometría, reconocer la posible existencia de acuíferos profundos, su desarrollo y la factibilidad de termalismo debido al gradiente geotérmico (3°C cada 100 m de profundidad). Se adquirieron, procesaron e invirtieron 121 estaciones gravimétricas dispuestas en cuatro perfiles y diez sondeosmagnetotelúricos (MT). Los resultados indican que la fosa se profundiza hacia el SE, alcanzando espesores sedimentarios que superan los 800 m. Por lo tanto, a partir de nuestros resultados se podría extraer agua entre los 800-900m de profundidad en dicha zona (SE). Los episodios arenosos o fracturados en profundidad podrían albergar aguas termales, cuya temperatura sería de aproximadamente 36 to 40°C a partir del gradiente geotérmico del país.

Layikeleke copper deposit is a large-scale porphyry copper polymetallic buried deposit, which has been discovered recently in the eastern Junggar area of Xinjiang. Mineralization occurred in the Late Silurian and Early Devonian with the copper body mainly confined to tonalite. To find new ore bodies, it is necessary to map the 3D spatial distribution of the tonalite. For this reason, we deployed audio-magnetotelluric (AMT) sounding in the research area, collected 26 profiles and 1198 measuring points, carried out 3D inversion calculations of off-diagonal elements in the impedance tensor data using the nonlinear conjugate gradient method, and obtained a 3D electrical structure model. The electrical structure reveals two groups of NW-SE trending middle and middle low resistivity anomaly zones, which intersect the high resistivity bedrock area in the northwest of the study area. Based on the electrical data, it can be inferred that the medium low resistance tonalite in the northern part of the study area is the host rock of the porphyry copper polymetallic deposit, which has been verified by borehole data. The results of 3D AMT inversion depict the spatial distribution and depth variation characteristics of the tonalite electrical structure model, providing a basis for further prospecting and exploration. Therefore, this method of identifying lithology by 3D inversion can provide an important basis for mineral exploration and mining of buried rock masses, and is an effective prospecting method.

The study of geothermal systems is nowadays a topic of great importance because of the huge amount of energy that could be converted in electricity for human consumption from such sources. Among the various geophysical methods employed to study geothermal reservoirs, the magnetotelluric (MT) method is capable to reveal the internal structures of the subsurface and interpret the geological structures from the electrical resistivity. We present the first 3D resistivity model of La Palma (Canary archipelago, Spain) obtained from a dataset of 44 broadband magnetotelluric soundings distributed around the island. Our results highlight the presence of resistivity anomalies, spatially coinciding with density anomalies present in literature. In the north of the island, a high resistivity anomaly can be interpreted as the signature of an old intrusive body beneath the Taburiente caldera. In the south, a complex resistivity structure around the Cumbre Vieja volcanic ridge could be indicative of presence of an active geothermal system. In particular, low-resistivity anomalies, located in a high-fractured zone, have values compatible with clay alteration caps (illite and illite–smectite). Such a result suggests the presence of hot rocks, or a dike system, heating fluids in the interior of Cumbre Vieja volcanic system.

On 21 May 2021 (UTC), an MW 7.4 earthquake jolted the east Bayan Har block in the Tibetan Plateau. The earthquake received widespread attention as it is the largest event in the Tibetan Plateau and its surroundings since the 2008 Wenchuan earthquake and in proximity to the seismic gaps on the east Kunlun fault. Here we use satellite interferometric synthetic aperture radar data and subpixel offset observations along the range directions to characterize the coseismic deformation of the earthquake. Rang offset displacements depict clear surface ruptures with a total length of ~170 km involving two possible activated fault segments in the earthquake. Coseismic modeling results indicate that the earthquake is dominated by left-lateral strike-slip motions of up to 7 m within top 12 km of the crust. The well-resolved slip variations are characterized by five major slip patches along strike and 64% of shallow slip deficit, suggesting a young seismogenic structure. Spatial-temporal changes of postseismic deformation are mapped from the early 6-day and 24-day InSAR observations, and are well explained by time-dependent afterslip models. Analysis of GPS velocity profiles and strain rates suggests that the eastward extrusion of plateau is diffusely distributed across the east Bayan Har block, but showing significant lateral heterogeneities as evidenced by magnetotelluric observations. The block-wide distributed deformation of the east Bayan Har block along with the significant co- and post-seismic stress loading from the Maduo earthquake imply high seismic risks on regional faults, especially the Tuosuo Lake and Maqin-Maqu segments of the Kunlun fault that known as seismic gaps.

SUMMARY The Tuareg Shield was assembled by oceanic closures and horizontal movements along mega-shear zones between approximately 20 terranes during the Pan-African Orogeny (750–550 Ma). Although there is an ongoing debate about its origin, the exhumation of the Tuareg Shield is assumed to be related to Cenozoic intraplate volcanism. The Gour Oumelalen is a key region of the Tuareg Shield and is located in the northeastern part of the Egéré-Aleksod terrane, corresponding to the eastern boundary of the Archean–Palaeoproterozoic microcontinent LATEA (Central Hoggar). The eastern boundary of the study area corresponds to a Neoproterozoic suture zone separating two old microcontinents, LATEA and the Orosirian Stripe. We deployed two magnetotelluric (MT) profiles consisting of 33 broad-band MT stations and combined these with aeromagnetic data, aiming to define the crustal structure in detail. The resistivity cross-sections obtained from the 3-D inversion of full impedance tensor and tipper data from stations along the profiles, confirm the main Precambrian faults, some of which are covered by Quaternary sediments and hence, have not yet been deciphered. The cross-sections also highlight the Cretaceous–Quaternary sedimentary basins represented by low resistivities. The upper crust is typically cratonic with a high electrical resistivity. On the contrary, the lower crust shows a drastic drop in resistivity (

One of the well-known geothermal potential areas in Iran is the Abgarm in Mahallat region. Due to existence of several hot springs, the Abgarm area is of particular importance in geothermal studies. To investigate the geothermal mechanism at Abgarm, geophysical surveys of magnetometry and magnetotelluric (MT) were utilized near hot springs to image the geometry of all geological requisites for trapping a geothermal reservoir. The ground magnetic data were inverted in 3D to construct a magnetic susceptibility model, where a deep intrusive igneous rock (as a heat source) and a shallow magmatic lava were inferred from the physical model. Euler depth estimation also provided insight to a shallow granodiorite unit embedded in a thick sequence of sediments. Dimensionality and strike analysis of the MT data were performed through the phase tensor method to investigate the general geometry of the sought reservoir for running a 2D TE + TM mode inversion scheme. Through 2D inversion of the MT data along three profiles across the favorable zones, the electrical resistivity models were used to image sedimentary units (i.e., cap rock, top soil, bedrock and reservoir) and magmatic rocks. Considering both geophysical properties led to illustrate a plausible geothermal reservoir in the area.

In this study, Shengli fault depression, Tangyuan fault basin, and northern Songliao Basin in Yitong-Yilan fault zone of Heilongjiang province are considered the research areas for geothermal anomaly. Based on the temperature of the deep thermal reservoir, the hydrothermal fluid channel, caprock thickness, and the mode of heat transfer, which are the main factors controlling the geothermal reservoir formation, we examined geothermal resource system of the underground HDR in this area. First, we inversed the aeromagnetic data, calculated the Curie isotherm depth, analyzed the geothermal distribution characteristics, and estimated the temperature of the deep heat source. Second, we applied the controlled source audio frequency magnetotelluric (CSAMT) and magnetotelluric (MT) methods to obtain the deep electrical structure of the study area. We determined the thickness of the caprock and the hydrothermal fluid channel. Finally, we obtained the borehole geothermal steady-state temperature measurement data and water sample chemical analysis data from the logging temperature curves of 24 wells to infer the mode of heat transfer. Based on the results, we built a model of the geothermal system of the sedimentary basin in this area. The results show that the depth of Curie isotherm in the study area is 17–39 km. The resistivity of sedimentary caprock in the north of Songliao basin is low, and there exists a deep heat source, which is mainly thermal convection. In contrast, in Shengli and Tangyuan fault basins, heat conduction is dominant. Based on the geothermal system model, we conclude that the area from Daqing to Lindian in Songliao basin has a thermal-convection-dominated sedimentary basin geothermal system. Heat exchange is realized by the upwelling of mantle-derived thermal materials through fracture channels. The thick sedimentary caprock reduces the heat loss. It can be a target for sustainable development and utilization of HDR.

Geothermal energy is a clean alternative energy resource. Southern Ogan Komering Ulu (OKU), South Sumatera, is a geothermal prospect area because of the interaction between the Eurasian and Indo-Australian tectonic plates. It causes geological structures growth and the activity of volcanism in the area. Based on geological data, geothermal in southern OKU is indicated by the existence of 40–93 oC temperature hot springs. Geological data based on remote sensing methods can determine the lineament. Geophysical data with gravity and magnetotelluric can identify the type of rock and the subsurface geological structure based on rock density and resistivity. Based on geological and gravity data indicates the presence of geological formations lead northwest-southeast, which is estimated as the geothermal fluid pathway with the suitability to the location of hot springs. The magnetotelluric data shows the geothermal reservoir rocks (clastic sedimentary rock) located at (-500)–(-2.500) meters depth with 30–200 Ωm resistivity. DOI: http://dx.doi.org/10.17977/um024v5i12020p022

The lithospheric mantle structure of the Antarctic continent is of great significance of studying the polymerization and fragmentation mechanism of Gondwana and the plate movement law. Long-period magnetotelluric (LMT) is an important method to study the electrical structure of earth crust and mantle. However, been limited by the bad natural environment and logistics supply difficulties, there is no LMT record of Antarctica before. In 2018, China's 34th Antarctic scientific expedition carried out the LMT survey at the eastern edge of the Antarctic continent with a frequency range of 0.00015 Hz to 0.1 Hz. After the processing and analysis, we get three points as fellow: (1) The lithospheric mantle of Antarctica has a three-dimensional resistivity structure; (2) There are low resistivity regions in the Antarctic mantle, which may be related to thermal activity. (3) It is possible to carry out LMT measurements in eastern Antarctic and more can be done in the future.

Two overlapping legacy seismic profiles, 130 km long end to end, were shot in the 1990s over the Kuruman Hills on the western margin of the Kaapvaal Craton in southern Africa. The 6‐s profiles were aimed at investigating the crustal structure of the western Kaapvaal Craton as well as to locate potential continuation of the Witwatersrand gold‐bearing horizons beneath the cover rocks, the latter of which was unsuccessful. In this study, the legacy seismic data are reprocessed and used to image the iron‐oxide (mainly haematite) mineralization found in the Kuruman Formation of the Griqualand‐West Supergroup, which outcrops along the two seismic profiles. The seismic profiles are located close to the Sishen open pit iron mine, where one of the world's largest iron ore concentrations (986 Mt) is mined. The reprocessed and merged seismic data are combined with magnetic, magnetotelluric, borehole and outcrop data to constrain the interpretation, and all indicate the mineralization host rocks to have ∼500 m thickness and 950 m depth. The seismic data further reveal seismic reflections associated with multiple iron ore horizons, which are affected by a first‐order scale syncline and numerous near‐vertically dipping (∼65–80°) normal and reverse faults of various orientations and throws, thus providing insight into the structurally controlled iron ore mineralization in the area. Seismic tomography and magnetotellurics characterize the sediments to have a velocity ranging between 5000 and 6000 m/s and a resistivity of

The last volcanic eruptions at the intraplate Wudalianchi volcanic field in northeast China were ∼300 yr ago. Recent ambient noise tomography (ANT) imaged a potential magma chamber beneath one of its volcanoes, the Weishan volcano, which last erupted at ca. 50 ka. To image the spatial distribution of the magmatic system and estimate the melt fractions beneath the Weishan volcano, we use a dense magnetotelluric (MT) network (average site spacing of ∼1 km) around the Weishan cone to image a three-dimensional (3-D) resistivity structure beneath the volcano. For the first time, 3-D MT inversion illuminates the high-resolution spatial distribution of a very low-resistivity body of ∼0.3–3 Ω·m at depth of ∼2–15 km beneath the Weishan volcano. From the 3-D resistivity model, it can be deduced there exists a magma chamber in the upper and middle crust. From both low-velocity anomalies from ANT and low-resistivity anomalies from MT imaging, melt fractions of magma reservoirs are reliably estimated to be >∼15%. From the morphology of magma reservoirs and the shallow magma chamber, the Weishan volcano can be best described by the model of transcrustal magmatic system. Considering the significant melt fractions and active earthquakes and tremors occurring around magma reservoirs, the Weishan volcano is likely in an active stage with magma recharging. Therefore, it needs more active monitoring for better forecasting of its potential future eruptions.

We present a case study on imaging volcanic units in gas exploration by constraining magnetic amplitude inversions using magnetotelluric (MT) sounding data at sparse locations. Magnetic data can be effective in mapping volcanic units because they have remanent magnetization and significant susceptibility contrast with surrounding rocks. Although magnetic data can identify the lateral distribution of volcanic units, they often have difficulties in defining the depth extent. For this reason, additional structural constraints from other geophysical methods can often help improve the vertical resolution. Among the independent geophysical methods, MT data can provide the needed structural information at a low cost. We have investigated an approach to combine a set of sparse MT soundings with magnetic amplitude data to image the distribution of volcanics in a basin environment. We first use a blocky 1D MT inversion based on Ekblom norm to obtain the structural constraint, and then we perform a constrained 3D magnetic amplitude inversion to recover the distribution of effective susceptibility by incorporating the structural information from MT soundings. We determine that even a small number of MT stations (e.g., 20) in a [Formula: see text] area is sufficient to drastically improve the magnetic amplitude inversion. Our results indicate that magnetic amplitude inversion with structural constraint from MT soundings form a practical and cost-effective means to map the lateral and vertical distribution of volcanics.

We investigated the magmatic–hydrothermal system of Aso Volcano, Japan, using broadband magnetotelluric (MT) data. To establish the nature of the shallow crust, a previous resistivity model based on data from 100 measurement sites in and around Aso volcano was revised using data from 9 additional sites near Naka-dake crater, which is located in the central part of the volcano. The components of MT impedance and the tipper vector were used to obtain the resistivity structure by three-dimensional inversion. The resistivity structure shows a subvertical low-resistivity (

A magnetotelluric acquisition and modelling campaign, comprising 400 full tensor soundings, was carried out in the Sub‐Andean Foothills in the area located south of Santa Cruz de la Sierra, Bolivia. The objective of the survey was to improve the imaging of the Paleozoic section and provide insight to the overall structure of the Devonian Silurian complex. The acquired data were inverted assuming both two‐dimensional and three‐dimensional dimensionality of the subsurface structure, adopting a multi‐step iterative workflow, which began applying unconstrained inversion and introduced increasing constraints determined at each following step based on the interpretation of the latest inversion results. The geological interpretation of the final inversion results allowed to better image the expected complexity in the structures, particularly highlighting several different levels of detachment, mainly in the area of Kirusillas Formation. Furthermore, an oblique sense was identified of the main tendency of N‐S deformation, related to a dextral transgressional movement that generates discrete dislocations, at a length scale of the order of a few kilometres.

Extension parallel to fold axis represents a rarely documented tectonic process that occur in different tectonic settings such as large-scale orogenic belts, mountain ranges, and thrust and fold belts. Along the Ecuadorian Andes, extensional systems have only been reported as tectonic boundaries of local intermontane basins, pull-apart depressions and outer-arc stretching faults along hinge surfaces in compressional antiforms. The Quito fault system shows in planform view a right-stepping en-echelon arrangement which southernmost anticlinal ridge terminates as an arcuate structure locally dissected by the Saguanchi Gorge. Valley hillslopes of this transverse drainage display evidence of tectonic extension featured by several swarms of normal faults commonly dipping towards the valley bottom. Magnetotellurics sounding obtained across a N‒S line parallel to the crestline axis reveals three contiguous and distinguishable domains of which the central one shows a wedge-shaped geometry pointing down. This tectonic evidence for ongoing extensional deformation suggests that the process of fold-axis-parallel extension controlled the tectonic development and dissection of the Saguanchi Gorge across the anticlinal ridge. This episode marks a significant change in the groundwater recharge and aquifer storage conditions between the Quito basin and the inter-Andean Depression aquifer systems, currently in production to provide the potable water supply for the Quito city.

The impact of untreated sewage irrigation and waste disposal practices on groundwater is investigated by 3D joint inversion of radio magnetotelluric and electrical resistivity tomography data. In this case study, electrical resistivity tomography and radio magnetotelluric field measurements were carried out on several profiles near a waste disposal site which was irrigated with untreated sewage water for agriculture purpose. In addition, radio magnetotelluric and electrical resistivity tomography measurements were carried out, far away from the waste site, to derive the uncontaminated geology. The data were analysed earlier using 2D inversion techniques. However, for the 2D inversion of the electrical resistivity tomography and radio magnetotelluric data, assumptions about the strike direction are required. As no clear strike direction is evident for the contamination, we considered the problem as 3D and interpreted the present data set using the 3D inversion algorithm ‘AP3DMT‐DC’. The inverted 3D resistivity model shows an unconfined aquifer of low resistivity which is overlain by an unsaturated slightly resistive near surface formation. With increasing distance from the waste sites, an increase in the resistivity of the shallow unconfined aquifer is observed. Furthest away from the waste site undisturbed geology is expected. We derived consistent and meaningful 3D resistivity models. The uncontaminated reference site indicates an increased resistivity for the aquifer layer. A synthetic 3D study was carried out to demonstrate and validate algorithm performance as well as convergence capabilities. The study demonstrates that the two methods, electrical resistivity tomography and radio magnetotelluric, complement each other. Besides, a better resolved inverted model is obtained through a 3D joint inversion, in comparison to individual 2D and 3D inversions.

Mapping the static gravity field in the Italian area is fundamental to identify the main lithospheric structures, to delineate the main geological elements at regional level and to infer the regional geodynamic setting. The ongoing tectonic processes highlight nevertheless the need to measure and model the time-variable gravity field, namely the dynamic gravity field, which requires increased accuracy and long time series of observations to separate the secular from the short-term variable components. The first, with a minor impact in Italy, are due to variations of ice mass balance (the viscoelastic response of the Earth to past changes in ice mass loading, and the elastic response of the Earth to present-day deglaciation), and the sea-level rise; the second are due to space/time variations of underground mass distributions, such as those related to seismic deformations, volcanic dynamics/eruptions and water transfer. Local-scale gravity studies along seismogenic faults may provide useful hints to study the seismic cycle and to unravel those areas more prone to seismic release by studying if the crustal volume is undergoing dilatancy (gravity decrease) or overpressure (gravity increase) before earthquake occurrence. This process, however, is accompanied by possible fluid migration, which can be revealed by other geophysical measurements, for example, by magnetotelluric and geoelectrical surveys. In this short paper, we briefly summarize the main sources of gravity variation providing on the same time orders of magnitude, spatial and temporal scales of their effects.

Earth, Planets and Space, 72 (1), ISSN:1343-8832, ISSN:1880-5981

SUMMARYTectonic activity is very difficult to study in the Santorini volcanic complex (SVC) as it comprises a cluster of small/awkwardly shaped islands covered by pyroclastic deposits from which tell-tale markers are swiftly erased, while seismicity is generally absent. We address the problem by combining geophysical exploration methods to evaluate the long-term effects of tectonic deformation and time-lapse differential GPS to directly evaluate the magnitude and kinematics of present-day deformation. The former comprise 3-D gravity modelling to investigate the footprint of tectonics on the pre-volcanic Alpine basement and natural-field EM induction to map conductivity anomalies epiphenomenal to fluid circulation in faults. Our analysis identified the following principal tectonic elements:The Trans-Santorin Divide (TSD), a segmented NNW–SSE dextral strike-slip fault splitting the SVC sideways of the line joining Cape Exomytis, the Kammeni Islets and the Oia–Therassia Strait. It is collocated with a major vertical conductive zone and forms a series of dents and depressions in the basement. The Columbo Fault Zone (CFZ) is a pair of parallel NE–SW subvertical normal-sinistral faults straddling the northern SVC and terminating against the TSD; it may be associated with fluid injection into the shallow crust but appears to have limited effect on crustal conductivity (compared to TSD). The Anhydros Fault Zone (AFZ) is detected by its footprint on the basement, as a set of parallel northerly dipping NE–SW faults between the Athinios–Monolithos line and Fira. If it has any heave, it is left-lateral. It does not have distinguishable electrical signature and does not contribute to present-day horizontal deformation. The CFZ and AFZ are antithetic and form a graben containing the volcanic centre of Kammeni Islets.E–W extension was identified lengthwise of a zone stretching from Cape Exomytis to Athinios and along the east flank of the caldera to Imerovigli. N–S normal faulting confirmed therein, may have contributed to the localization of the east caldera wall. NNE–SSW compression was observed at SW Thera; this may have produced E-W failure and contributed to the localization of the south caldera wall. The footprint of the caldera on the basement is a parallelogram with N–S long and WNW–ESE short dimensions: if the east and south flanks collapsed along N–S normal and E–W inverse failures, then the west and north flanks may have formed analogously. Present-day deformation is localized on the TSD and CFZ: this can only be explained if the former is the synthetic (dextral) Riedel-R shear and the latter the antithetic (sinistral) Riedel-R′ shear, generated by N–S σ1 and E–W σ3 principal stress axes. Accordingly, NW–SE right-lateral shearing of the broader area is expected and indicated by several lines of indirect evidence. The geographic extent of this shearing and its role in the regional tectonics of the south Aegean remains to be confirmed and appraised by future research.Contemporary volcanic centres develop at the interface of the TSD with the CFZ/AFZ graben; volcanism appears to be controlled by tectonics and the SVC to be shaped by tectonic rather than volcanic activity.

The terrain conditions and geological structure of the mountainous areas in western China are complex. To meet the design requirements for the expressway, the route adopts the design of deep-buried super-long tunnels in hilly areas. If the highway tunnel passes through faulty structures, such as improper selection of structure and foundation form, it can cause collapse and structural instability during construction. Therefore, basic characteristics of faults and information that is more accurate should be provided during the survey process to avoid subsequent problems. The frequency and magnitude of earthquakes in this study area are high and available data show that the Xiaojiang fault was still active during the Quaternary Holocene period, which is a high-risk area for earthquakes. Therefore, a set of comprehensive technologies, such as geophysical prospecting, geological survey, and drilling, and was used to identify faults and their characteristics and to visually display underground information within a certain depth range. Here, the magnetotelluric method was used to analyze the electrical characteristics and structure of the highway tunnel. In addition, the electrical characteristics and structure of the Xiaojiang fault were discussed. Geological surveys and drilling agree well with the analysis and interpretation of the research results and further proposed a processing and interpretation method for correcting the dip angle of the fault using the statistical results from the long axis dip angle of the tensor polarization map for the wave impedance. Thus, a large amount of information in the tunnel site can be effectively obtained for predicting and evaluating the Xiaojiang fault. Furthermore, our results provide strong technical support for designing and operating highway tunnels, with meaningful experience and reference for future geophysical processing and interpretation.

The Lushi gold polymetallic ore-concentration area, located in the southern margin of North China Craton, is an important polymetallic ore district in the Qinling metallogenic belt. The Jianbeigou gold deposit is an important quartz vein type gold deposit in this district. In order to reveal the geological structure of the Jianbeigou gold deposit to guide deep prospecting, the EH4 conductivity image system was used in the Jianbeigou area. The sections obtained by the audio magnetotellurics method (AMT) indicate that the steeply dipping low resistivity zone in the area has a good corresponding relationship with the location of the known shallow ore bodies, and an extension in the deep. The low resistivity anomaly zone obtained by the inversion results are well correlated with the gold mineralization zone of the ore bodies, indicating good deep prospecting and exploration potential in this area. Based on geological and geophysical evidences, this paper inferred the possible occurrence location and depth range of the buried ore bodies. The AMT survey results reflect good exploration potential of the mining area and provide a geophysical basis for deep prospecting.

The tectonic history of Southern Africa includes Archean formation of cratons, multiple episodes of subduction and rifting and some of the world's most significant magmatic events. These processes ...

Magnetotellurics (MT) is an important geophysical method for exploring geothermal systems, with the Earth resistivity obtained from the MT method proving to be useful for the hydrothermal imaging changes of the system. In this research, we applied the MT method to map the geothermal system of the Seulawah Agam volcano in northern Sumatra, a site intended for the construction of a geothermal power plant with an estimated energy of 230 Mwe. Herein, 3D MT measurements were carried out, covering the entire area of the volcano and the various intersecting local faults from the Seulimeum segment in the NW–SE direction. Based on Occam 2D inversion, a conductive anomaly (&lt, 10 ohm·m) near the surface was identified in response to specific manifestation areas, including the Heutsz crater on the northern side and the Cempaga crater on the southern side. A further conductive anomaly was also found at a depth of 1 km, which was presumably due to a clay cap layer covering the fluid in the reservoir layer below the surface, where the manifestation areas are formed at various locations (where faults and fractures are found) owing to the fluid in the reservoir rising to the surface. The MT modeling also revealed that the reservoir layer in Seulawah Agam lies at a depth of 2 km with a higher resistivity of 40–150 ohm·m, which is the main target of geothermal energy exploration. At the same time, the heat source zone where magma is located was estimated to lie in two locations, namely, on the northern side centering on the Heutsz crater area and the southern side in the Cempaga crater area. A clear 3D structure obtained via Occam inversion was also used to visualize the hydrothermal flow in the Seulawah Agam volcano that originates from two heat source zones, where one structure that was consistent across all models is the conductive zone that reaches a depth of 5 km in the south in response to the regional faulting of the Seulimeum segment. Based on the MT research, we concluded that the volcano has the geothermal potential to be tapped into power plant energy in the future.

The Songpan−Aba region is located on the northeastern edge of the Tibetan Plateau. Tectonically, the area is surrounded by the West Qinling orogenic belt in the north, the Longmenshan orogenic belt in the southeast, and the East Kunlun and Sanjiang orogenic belts in the west and southwest, forming a triangle that provides an ideal location to study the crust-mantle structure and deep tectonics of the eastward extrusion of the Tibetan Plateau. In this study, the magnetic and electrical structures of the Songpan−Aba area were investigated by inversion using high-precision magnetic anomaly and magnetotelluric data to obtain the subsurface magnetization inversion intensity and resistivity of Songpan–Aba and adjacent areas. The results revealed a continuous magnetic layer up to 20 km below Songpan–Aba and its surrounding areas in the south, possibly originating from a magma root southwest of the Longmenshan massif. In the West Qinling, Songpan–Aba, and Longmenshan areas, pervasive low-resistance, weakly magnetic, or magnetic layers were identified below 20 km that might be formed from the molten mantle material extruded from the eastern edge of the Tibetan Plateau.

Study region The study area is located at Kapunda, South Australia with a semi-arid climate and comprises a fractured rock aquifer. Established in 1842, Kapunda was the first mining town in Australia and its open-pit mine was a key economic driver for the whole continent. The mine was closed in 1879 and the remnant low-grade copper was considered sub-economic, hence the mine has been developed into a tourist attraction. With the recent advances in In-Situ Recovery (ISR), the feasibility of recovering the remnant copper is under consideration again. Study focus A field trial involving lixiviant injection and extraction is under development. This study uses a combination of stochastic groundwater modeling and multiple geophysical techniques to investigate (1) the flow paths of injectant and whether it will reach the Light River, and (2) the injectant residence time in the aquifer. New hydrological insights for the region Depending on the effective porosity of the aquifer, the modeling suggests a probability of 1 %–5 % for the injectant to escape the site. There is a large uncertainty in the simulated injectant residence time, ranging from 200 to beyond 1000 days. These analyses are conservative and do not consider the biodegradability of the injectant, which can achieve a 90 % degradation over 28 days. Our modeling shows no evidence that the injectant can reach the Light River within this timeframe.

Details on the 3-D magnetotelluric inversion, sensitivity test of resistivity anomalies and melt fraction estimation, and Figures S1–S11.

This paper presents results from a magnetotelluric survey at Ceboruco Volcano in Mexico. The observed data require an anisotropic 3-D electrical resistivity model which links a near-surface geothermal reservoir to the magmatic system and finally to the local tectonic setting. Ceboruco is an active stratovolcano, which is located in the Tepic-Zacoalco Rift and is part of the Trans-Mexican Volcanic Belt. Together with Chapala and Colima, the Tepic-Zacoalco Rift forms a triple rift system, which developed as a consequence of the subduction of the Rivera and Cocos oceanic plates beneath the North American continental crust. Ceboruco is the largest and most active volcano in the region. Broadband magnetotelluric data were collected at 25 sites distributed on and around Ceboruco Volcano during a two-week campaign. The survey focused on the electrical resistivity distribution to characterize the geothermal potential and the deep structure beneath the volcano. The data quality is very high in a wide period range between 10−4 and 102 s and there is a consistent data pattern at all sites. For stations on top of the volcano, topographical effects dominate the shortest periods, whereas a highly conductive layer is implied for periods below 1 s. A spatially constant phase split and coincident small induction vectors are observed to the long period end. The 3-D isotropic inversion of the data yields an excellent data fit for short and intermediate periods and reveals a shallow magma storage and an extensive hydrothermal reservoir between 1 km a.s.l. and approximately 2 km b.s.l. At greater depth, the inversion algorithm generates large-scale high resistivity contrasts, reaching far outside the area of investigation. The resulting structures are inconsistent with the known geological setting and are considered to be artifacts of the isotropic inversion. We present an alternative model, which includes two anisotropic layers below 10 km depth. The conductive principal axes of the anisotropy are consistent with the local rifting direction in the Tepic-Zacoalco Rift and relate to a ductile deformation of the host rock and a large mush zone at mid- to lower-crustal depths.

Geothermal manifestations (hot springs) emerge in the Al-Mubazzarah Geothermal Area (AMGA), Al-Ain city, Abu Dhabi Emirate, United Arab Emirates. This paper presents the application and results of a Magnetotelluric (MT) survey, which was carried out in 2017 at the AMGA geothermal field. The MT method was used to investigate the variations in the electrical conductivity beneath the AMGA. This study focuses on characterizing the patterns of subsurface electrical conductivity of the AMGA geothermal reservoir. Dimensionality analysis of the measured MT data indicate that 2D inversion is appropriate for the subsurface resistivity interpretation. The inversion results support a model consisting of three resistivity-defined layers; from top to bottom they are: (1) a shallow layer with resistivity ranging from 10 to 20 Ωm, representing recent alluvial and windblown deposits, (2) a second conductive layer with resistivities less than 10 Ωm, beneath the first layer. This layer is recognized as the Tertiary carbonate sequence in the region, (3) a deep, moderate to relatively high resistive zone, 10–30 Ωm beginning at 800 m depth and reaching 4 km depth in the northern part of the profile, representing Mesozoic basement rocks. The observed moderate to high resistivity zone (10–30 Ωm) in the 2D model may represent a region where the hot groundwaters originated (geothermal reservoir), with the hottest geothermal located at a depth greater than 4 km. The geothermal reservoir zone is also represented by a low to high density contrast and a low to moderate magnetic susceptibility, as indicated in the inverted potential field data models, and confirmed the existence of a north dipping major fault., Magnetotelluric; Potential field; 2D inversion; geothermal; AMGA, Low-enthalpy, Al-Ain; United Arab Emirates.

Magnetotelluric (MT) data has been collected along 32 stations along E–W profile in northern part and eight LMT (long period MT) stations in north-central part of Saurashtra region. Dimensionality analysis is carried out prior to MT modelling for obtaining the subsurface dimension as well as the direction of the underlying substructures. To estimate the subsurface dimensionality from MT data, different techniques Swift skew, Bhar’s skew, normalized weights, phase tensor (PT) analysis and Wall’s rotational invariant approach have been applied. These results suggest 1D structure for lower periods (0.01–1 s) and 3D structure for higher periods (1–10000 s) along two different profiles indicating that the study area is highly heterogeneous. Regional strike has been estimated through phase tensor (PT) and Groom–Bailey (GB) techniques suggests N40°E regional strike direction that correlates well with the Delhi–Aravalli tectonic trend. 2D modelling of MT/LMT data sets brings out different resistivity and conductivity blocks. Basaltic magmatic intrusion and its recrystallization have resulted in resistivity blocks with conductivity anomalies (trapped fluids) in between them. It has been reflected as 3D structures at higher periods. Different sedimentary basins at shallow depth are observed as 1D structure in dimensionality analysis.

The Delhi Seismic Zone (DSZ) is a seismically highly active intraplate region that keeps experiencing recurrent seismicity of minor to moderate nature. The seismic activity in the DSZ in recent times has evoked concerns about the vulnerability of the region due to potential earthquakes. Although the spatial distribution of recorded earthquakes gives a fairly good idea about the zone of the seismicity, the information about the underlying crustal structure and seismogenic faults is largely missing. In the present work, we have revisited the MT data acquired at various locations across Haryana to understand whether there are any anomalous features in the crust that might correlate with the seismicity in the western part of the DSZ. The MT data recorded at six groups of sites yielded good impedance tensors in the period range of 0.001–1000 s. A significant result obtained by 2-D inversion of distortion corrected impedance tensors is the presence of a northward dipping electrical conductor (

We present results of 334 ultra-wide band MT stations across an area of 100 km × 100 km in the prospective eastern Gawler Craton. The survey area is situated ~100 km south of the supergiant Olympic...

The Hidaka collision zone, the collision boundary between the NE Japan and Kurile arcs, is known to be an ideal region to study the evolution of island arcs. The hypocenter of the 2018 Hokkaido Eastern Iburi earthquake (Mw 6.6) in the western part of the Hidaka collision zone was unusually deep for an inland earthquake, and the reverse fault that caused the earthquake has an uncharacteristically steep dip. In this study, we used three-dimensional inversion to reanalyze broadband magnetotelluric data acquired in the collision zone. The inverted resistivity model showed a significant area of high resistivity around the center of the collision boundary. We also identified a conductive zone beneath an area of serpentinite mélange in a zone of high P–T metamorphic rocks west of the high-resistivity zone. The conductive zone possibly reflects areas rich in pore fluids related to the formation and elevation of the serpentinites. Sensitivity tests indicated the need for additional magnetotelluric survey data to delineate the resistivity distribution around the epicentral area of the 2018 earthquake although the resistivity model showed a conductive zone in this area.