Magnetotelluric Survey Research Articles

Magnetotelluric imaging of the resurgent caldera on the island of Ischia (southern Italy): inferences for its structure and activity

The island of Ischia (located in the Bay of Naples, Italy) represents a peculiar case of a well-exposed caldera that has experienced a large (>800 m) and rapid resurgence, accompanied by volcanic activity. What drives the resurgence of calderas is a crucial issue to investigate, because this process is associated with potential eruptions and high risk to people living within and around such large active volcanic systems. To improve the knowledge of volcano-tectonic processes affecting the caldera of Ischia, electromagnetic imaging of the structures associated with its resurgence was performed and integrated with available geological information. A magnetotelluric (MT) survey of the island was carried out along two main profiles through the central-western sector, providing an electrical resistivity map to a depth of 3 km. These resistivity cross sections allowed us to identify the presence of a very shallow magmatic intrusion, possibly a laccolith, at a depth of about 1 km, which was responsible for both the resurgence and the volcanic activity. Furthermore, the tectonic structures bordering the resurgent area and the occurrence of a large thermal anomaly in the western sector of the caldera also provided a signature in the resistivity cross sections, with the magma intrusion producing advection of hot fluids with high geothermal gradients (>150 °C km−1) in the southern and western sectors. All of these data are fundamental for the assessment of the island’s volcano-tectonic dynamics and their associated hazards. The structure and activity of the island have been controlled by the process of resurgence associated with the arrival of new magma and the progressive intrusion of a laccolith at a shallow depth. The reactivation of such a shallow system may imply imminent eruption which would pose a major volcanic hazard.

3D joint inversion of magnetotelluric and airborne tipper data: a case study from the Morrison porphyry Cu–Au–Mo deposit, British Columbia, Canada

ABSTRACTZ‐axis tipper electromagnetic and broadband magnetotelluric data were used to determine three‐dimensional electrical resistivity models of the Morrison porphyry Cu–Au–Mo deposit in British Columbia. Z‐axis tipper electromagnetic data are collected with a helicopter, thus allowing rapid surveys with uniform spatial sampling. Ground‐based magnetotelluric surveys can achieve a greater exploration depth than Z‐axis tipper electromagnetic surveys, but data collection is slower and can be limited by difficult terrain. The airborne Z‐axis tipper electromagnetic tipper data and the ground magnetotelluric tipper data show good agreement at the Morrison deposit despite differences in the data collection method, spatial sampling, and collection date. Resistivity models derived from individual inversions of the Z‐axis tipper electromagnetic tipper data and magnetotelluric impedance data contain some similar features, but the Z‐axis tipper electromagnetic model appears to lack resolution below a depth of 1 km, and the magnetotelluric model suffers from non‐uniform and relatively sparse spatial sampling. The joint Z‐axis tipper electromagnetic inversion solves these issues by combining the dense spatial sampling of the airborne Z‐axis tipper electromagnetic technique and the deeper penetration of the lower frequency magnetotelluric data. The resulting joint resistivity model correlates well with the known geology and distribution of alteration at the Morrison deposit. Higher resistivity is associated with the potassic alteration zone and volcanic country rocks, whereas areas of lower resistivity agree with known faults and sedimentary units. The pyrite halo and ≥0.3% Cu zone have the moderate resistivity that is expected of disseminated sulphides. The joint Z‐axis tipper electromagnetic inversion provides an improved resistivity model by enhancing the lateral and depth resolution of resistivity features compared with the individual Z‐axis tipper electromagnetic and magnetotelluric inversions. This case study shows that a joint Z‐axis tipper electromagnetic–magnetotelluric approach effectively images the interpreted mineralised zone at the Morrison deposit and could be beneficial in exploration for disseminated sulphides at other porphyry deposits.

Identifying mineral prospectivity using 3D magnetotelluric, potential field and geological data in the east Kimberley, Australia

Abstract An integrated interpretation of the east Kimberley, northern Western Australia was completed to determine mineral prospectivity, and was centred on a portion of a magnetotelluric (MT) survey conducted across the entire Kimberley Craton and surrounding orogens. A structural geophysical interpretation used potential field data, and was constrained by geological field observations, petrophysics, remote sensing and understanding of the tectonic history of the region. Potential field forward modelling located along the same survey traverse as the MT data allowed comparison between the two datasets and their interpretations revealing interesting features suggesting the presence of large-scale structures, the presence of mineralization deep in the crust, and where mineralization may be at or near the surface. The King River Fault is shown from both the MT inversion and potential field modelling as a crustal-scale, west-dipping structure, the footwall of which bounds the western side of a large resistive body. A conductive anomaly is also located on the hanging wall of the King River Fault. Our assessment suggests that graphitic rocks, most likely with some sulphide content, contribute to the strength of this anomaly, and highlights the potential of the east Kimberley to host graphite and base metal deposits.

Modeling Geoelectric Fields and Geomagnetically Induced Currents Around New Zealand to Explore GIC in the South Island's Electrical Transmission Network

AbstractTransformers in New Zealand's South Island electrical transmission network have been impacted by geomagnetically induced currents (GIC) during geomagnetic storms. We explore the impact of GIC on this network by developing a thin‐sheet conductance (TSC) model for the region, a geoelectric field model, and a GIC network model. (The TSC is composed of a thin‐sheet conductance map with underlying layered resistivity structure.) Using modeling approaches that have been successfully used in the United Kingdom and Ireland, we applied a thin‐sheet model to calculate the electric field as a function of magnetic field and ground conductance. We developed a TSC model based on magnetotelluric surveys, geology, and bathymetry, modified to account for offshore sediments. Using this representation, the thin sheet model gave good agreement with measured impedance vectors. Driven by a spatially uniform magnetic field variation, the thin‐sheet model results in electric fields dominated by the ocean‐land boundary with effects due to the deep ocean and steep terrain. There is a strong tendency for the electric field to align northwest‐southeast, irrespective of the direction of the magnetic field. Applying this electric field to a GIC network model, we show that modeled GIC are dominated by northwest‐southeast transmission lines rather than east‐west lines usually assumed to dominate.

Mapping fluids to subduction megathrust locking and slip behavior

AbstractIn subduction zones, high fluid content and pore pressure are thought to promote aseismic creep, whereas well‐drained conditions are thought to promote locking and failure in earthquakes. However, observations directly linking fluid content and seismic coupling remain elusive. Heise et al. (2017, https://doi.org/10.1002/2017GL074641) use a magnetotelluric survey to image the electrical resistivity structure of the northern Hikurangi subduction thrust to ~30 km depth, as an indicator of interconnected fluid content. The authors document a clear correlation between high resistivity and a distinct geodetically locked patch and between conductive areas and weak coupling. Their study, together with other recent geophysical investigations, provides new evidence for the role of fluids in governing subduction thrust locking.

Magma storage beneath Grímsvötn volcano, Iceland, constrained by clinopyroxene‐melt thermobarometry and volatiles in melt inclusions and groundmass glass

AbstractBasalt eruptions at Grímsvötn volcano, Iceland, are generally of low intensity; however, occasionally, an order of magnitude larger eruptions occur. In order to discuss the reasons for this difference, the degassing budget of S and Cl and crystallization conditions of the eruptive magma were determined from volatile concentration measured in melt inclusion (MI) and groundmass glass and thermobarometry, respectively. Tephra of two of the largest historical eruptions (2011 and 1873) and two much smaller eruptions (2004 and 1823) were investigated. Sulfur and Cl concentrations are higher in groundmass glass of the smaller eruptions due to incomplete outgassing caused by melt quenching in contact with glacial water. Sulfur concentration and degassing budget correlate with erupted magma volumes. Higher volatile concentrations of MI from the larger eruptions reflect important recharge of gas‐rich magma from depth. The recharge causes a high‐magnitude eruption followed by increased eruption frequency over the following decades. Pressure and temperature estimates of crystallization are obtained through equilibrium clinopyroxene‐glass pairs, where crystals adjacent to, and in textural equilibrium with, both groundmass glass and that of MI were measured. An average crystallization pressure of 4 ± 1 kbar corresponding to approximately 15 ± 5 km depth was obtained together with a considerable temperature range, 1065–1175°C. Similar crystallization depths are obtained for the basalt of the 2014–2015 Bárðarbunga rifting event and to a low resistivity layer revealed by magnetotelluric surveys. Therefore, an important magma storage depth is inferred at lower crustal depth above the center of the Iceland mantle plume.

Development of an updated geothermal reservoir conceptual model for NW Sabalan geothermal field, Iran

In this paper, a conceptual model has been developed for NW Sabalan geothermal field using exploration indicators. These indicators include the data and results of subsurface and surface investigations comprising geology, geophysics , hydro-geochemistry, hydrology and temperature and pressure distribution. The subsurface information was obtained from 10 deep exploration wells as well as from the results of previous studies in this field. All available data together with the stratigraphy and 1:20,000 geological map covering the study area were combined to produce a two-dimensional geological cross section. Also, a subsurface three-dimensional geological model was developed using available drilling logs. NW Sabalan geothermal field is one of the 18 detected potential areas in Iran that is located in Northwest of the country. This field includes a deep geothermal reservoir with a temperature range of 230–242 °C. The reservoir is covered by a cap rock with an approximate thickness of 500 m. There are four major geological units identified in the study area including Quaternary alluvium, fan and terrace deposits; Pleistocene post-caldera trachyandesitic Flows; Pleistocene syn-caldera trachydacitic to trachyandesitic domes and Pliocene pre-caldera trachyandesitic lavas, tuffs and pyroclastic. A hydraulic conductivity zone has been assessed by magnetotelluric surveys at deeper zones, suggesting that the main outflow direction is towards west and north of the area. The fluid chemistry is consistent with high chloride, neutral pH and immature liquids that partially equilibrated with host rock and they are classified as mixed water. The results of exploration and geological studies during a 10-year period have been integrated together to build a new overall conceptual model of the field.

3-D magnetotelluric imaging of the Phayao Fault Zone, Northern Thailand: Evidence for saline fluid in the source region of the 2014 Chiang Rai earthquake

Seismicity in Thailand had been relatively low for decades prior to the Mw 6.5 earthquake of 5 May 2014 which came as a surprise and was followed by thousands of aftershocks. Most of the epicenters were located in the transition region between the Mae Lao Segment (MLS) and the Pan Segment (PS) of the Phayao Fault Zone (PFZ). We conducted a 3-D magnetotelluric (MT) survey (31 sites) to image the deep PFZ structure. The shallow 3-D resistivity structure matches very well with the surface geology, while the deeper structures disclose many interesting resistive and conductive anomalies. However, the most interesting feature of this study is the large conductive anomaly (ML) located at a depth of 4km to the mid-crust beneath the MLS near the seismogenic zone. Our current hypothesis is that the ML conductor has a highly interconnected aqueous fluid content and also plays crucial role in the earthquake sequence of the 5 May 2014 event. As our previous seismic waveform study revealed that the MLS has a relatively high fault plane instability, the fluid within the fractured fault would further reduce the fault strength. The accumulated pre-existing tectonic stress from the north can therefore overcome the maximum frictional strength of the MLS, and hence cause it to slip and produce the main shock. With the local structural heterogeneities and fluid in the fractured fault zones, the aftershocks then occurred on both the PS and MLS. This is in contrast to the Mae Chan Fault Zone (MCFZ) in the north which many scientists expected to generate a larger magnitude earthquake than any other faults. Since instrumental record, it has only generated a few Mw 4 earthquakes. Some of our MT stations were located within the MCFZ. However, there is no deep conductor as the conductor lies beneath the MLS. A lack of interconnected fluid within the deep fault beneath the MCFZ might be one of the reasons for the lower seismic activity from the MCFZ. Other geophysical methods, such as seismic tomography, are necessary in order to confirm the presence of the fluid beneath the MLS and also the lack of a deep conductor beneath the MCFZ.

Resistivtiy Structure in Tangkuban Parahu Area Drived from CSAMT Data

Tangkuban Parahu is located in Bandung, West Java, one of a volcano area. Controlled-source audio frequency magnetotelluric (CSAMT) survey has been conducted in the area using transmitter located in 3-5 km from the survey area. The objective of the survey was to determine a subsurface resistivity structures that may correlate to a geothermal reservoir in unknown geothermal potential area. In the paper, we applied a two-dimensional (2D) inversion scheme to interpret of the CSAMT data to obtain several resistivity sections describing the subsurface resistivity structures. The results of 2D inversion indicated several subsurface low resistivity anomaly (1-10 ohm.m) in the depth of 1000-1500 meter that may correlate to the existing a geothermal reservoirir confirmed by several surface manifestations in the area.

Magnetotelluric (MT) and Resistivity Survey along Belsara-Rasunpur Traverse Delineating Conductivity Structure over Bakreswar Geothermal Region in Birbhum District, West Bengal

Magnetotelluric (MT) and Resistivity Survey along Belsara-Rasunpur Traverse Delineating Conductivity Structure over Bakreswar Geothermal Region in Birbhum District, West Bengal

3D magnetotelluric exploration of Sete Cidades Volcano, São Miguel Island, Azores

Geothermal energy accounts for 43% of the electricity expenditure of São Miguel Island, Azores Archipelago. All production comes from the Ribeira Grande (RG) high-enthalpy geothermal field. To meet the growing energy demand in the island, it is necessary to extend the exploration efforts to new areas. We evaluated the results of a broadband magnetotelluric reconnaissance survey conducted at Sete Cidades Volcano, placed only 30 km westward of the RG field. The resistivity structure of the Sete Cidades geothermal system was obtained through a simultaneous 3D inversion of the full impedance tensor and tipper. The bathymetry and the topography of the island were treated as fixed features in the model. The geothermal reservoir at Sete Cidades is outlined as a northwest–southeast elongated resistive anomaly, geologically controlled by the Terceira Rift fracture zone. We have also identified high-conductivity zones between 1000 and 4000 m below mean sea level, probably associated with clay cap rocks overlying the geothermal reservoir.

WSJointInv2D-MT-DCR: An efficient joint two-dimensional magnetotelluric and direct current resistivity inversion

An efficient joint two-dimensional direct current resistivity (DCR) and magnetotelluric (MT) inversion, referred to as WSJointInv2D-MT-DCR, was developed with FORTRAN 95 based on the data space Occam's inversion algorithm. Our joint inversion software can be used to invert just the MT data or the DCR data, or invert both data sets simultaneously to get the electrical resistivity structures. Since both MT and DCR surveys yield the same resistivity structures, the two data types enhance each other leading to a better interpretation. Two synthetic and a real field survey are used here to demonstrate that the joint DCR and MT surveys can help constrain each other to reduce the ambiguities occurring when inverting the DCR or MT alone. The DCR data increases the lateral resolution of the near surface structures while the MT data reveals the deeper structures. When the MT apparent resistivity suffers from the static shift, the DCR apparent resistivity can serve as a replacement for the estimation of the static shift factor using the joint inversion. In addition, we also used these examples to show the efficiency of our joint inversion code. With the availability of our new joint inversion software, we expect the number of joint DCR and MT surveys to increase in the future.

P1-33 比抵抗構造から推定される立山地獄谷の熱水系(ポスターセッション)

P1-33 比抵抗構造から推定される立山地獄谷の熱水系(ポスターセッション)

An integrated magnetotelluric and gamma exploration of groundwater in fractured granite for small-scale freshwater supply: a case study from the Boshan region, Shandong Province, China

Exploration and use of groundwater in hard rocks is a difficult but yet a significant issue, especially when the local surface water source is polluted. In this study, integrated geophysical and nuclear methods are used to delineate groundwater-bearing zones in a granite terrain in the Boshan region, Shandong Province, China. Structural analysis showed that fractures extend in a NW–SE direction, which is the same as the direction of river valley. A controlled source audio-frequency magnetotelluric survey conducted along the river valley indicated several different low resistivity anomalies or potential water-bearing fracture zones. They are seated at depth ranges down to 400 m from the surface along the river valley. The locations of deep water-bearing zones were further confirmed by higher gamma radiation measurements found near the river valley. A fault with a NW–SE strike near the river was deduced as an anomalous water-bearing zone. Two tube wells were drilled targeting at the water-bearing zone that has achieved single-well water yield greater than 360 m3/day. The well water was sampled for water chemistry and stable isotope analyses. Shallow groundwater samples show similar water chemistry and isotopic feature to river water, indicating connection between the two. Deep groundwater from the water-bearing fracture zones is not hydraulically connected with shallow groundwater, ensuring safety of the deep groundwater in the granite from being affected by the polluted shallow groundwater or river water. Integrated geophysical and gamma exploration methods helped to identify two disconnected groundwater systems, offering an alternative freshwater source for the region if shallow groundwater or surface water is polluted.

Effect of graphite on the electrical conductivity of the lithospheric mantle

AbstractGraphite is considered as one of candidate to explain the high‐conductivity anomalies revealed through magnetotelluric (MT) observations. To investigate the effect of interfacial energy on the interconnection of graphite in olivine matrix, we measured the electrical conductivity of polycrystalline San Carlos olivine mixed with 0.8 vol % graphite on the grain boundaries via impedance spectroscopy at 1 GPa and 300–1700 K in a cubic multianvil apparatus. The olivine‐graphite dihedral angle of the recovered sample was also measured to determine interfacial energy between graphite and olivine. The bulk electrical conductivities and large activation enthalpy (∼1.32 eV) of the carbon‐bearing sample were consistent with those of dry polycrystalline olivine. This behavior implies that graphite cannot be interconnected on olivine grain boundaries, which is also supported by the large dihedral angle (98°) of the olivine/graphite system. Impedance spectroscopy measurements were performed at 3 GPa and a temperature of up to 1700 K for carbon‐coated olivine bicrystal samples to investigate the stability of graphite films on the grain boundaries of silicate minerals under upper‐mantle conditions. The conductivities rapidly or slowly dropped as a function of time and graphite film thickness during annealing at the target temperature. This phenomenon exhibits that graphite film on the olivine grain boundary is readily destroyed under upper‐mantle conditions as supported by microstructural observations on the recovered carbon‐coated olivine bicrystal samples. Higher interfacial energy and larger dihedral angle (∼98°) between graphite and olivine would not allow the maintenance of graphite film on olivine grain boundaries. The activation enthalpy for the apparent disconnection rate of a graphite film on olivine grain boundaries is close to that of carbon diffusion in olivine grain boundaries, which suggests that the disconnection of the graphite film is likely to be controlled by carbon grain boundary diffusion. Therefore, graphite is an unlikely candidate to explain the high‐conductivity anomalies revealed by MT surveys in the upper mantle.

Controlled Source Audio Magneto Telluric (CSAMT) Studies for Uranium Exploration in Durgi Area, Palnad Sub-basin, Cuddapah Basin, India

ABSTRACT Cuddapah basin is known for hosting unconformity proximal uranium deposits viz., Lambapur, Peddagattu, Chitirial and Koppunuru along the northern margin of the basin. It is well known that these deposits are mostly associated with basement granitoids in Srisailam Sub-basin, and with cover sediments in Palnad sub-basin where basement topography and fault/fracture system influence the fluid flow causing basement alteration and ore deposition. Geological setup, surface manifestation of uranium anomalies and association of the hydro-uranium anomalies near Durgi area in southern part of the Palnad sub-basin, have prompted detail investigation by geophysical methods to probe greater depths. Controlled Source Audio Magneto Telluric (CSAMT) survey conducted over five decades of frequency (0.1-9600 Hz) delineated the various lithounits of Kurnool and Nallamalai Groups along with their thicknesses as there exist an appreciable resistivity contrast. Interpretation of CSAMT sounding data are constrained by resistivity logs and litholog data obtained from the boreholes drilled within the basin indicated three to four layered structure. Sub-surface 2-D and 3-D geo-electrical models are simulated by stitching 1-D layered inverted resistivity earth models. Stitched 1-D inverted resistivity sections revealed the unconformity between the Kurnool Group and Nallamalai Group along with basement undulations. The faults/fractures delineated from the CSAMT data corroborated well with the results of gravity data acquired over the same area. Simulated 3-D voxel resistivity model helped in visualising the faults/fractures, their depth extent, thickness of the Banganapalle quartzite and basement configuration. Integrated interpretation of CSAMT, gravity and borehole data facilitated in delineating the unconformity and the structural features favourable for uranium mineralisation in deeper parts of the Palnad sub-basin.

Electromagnetic evidence for volatile‐rich upwelling beneath the society hotspot, French Polynesia

AbstractWe have conducted a seafloor magnetotelluric survey that images, for the first time, three‐dimensional electrical conductivity structure in the upper mantle beneath the Society hotspot. A striking feature in our model is a high‐conductivity anomaly a few hundred kilometers in diameter, which is continuous from the lowest part of the upper mantle to a depth of approximately 50 km below sea level. Using theoretical and experimental results from mineral physics, we interpret the high‐conductivity anomaly as evidence of the melt fraction up to 2.2 vol.%, which is robust regardless of assumed temperature, and the existence of carbonated silicate melt beneath the hotspot. Our results suggest that the Society hotspot is a pathway for ascending volatiles from the deeper part of the upper mantle to the surface.

Magnetotelluric monitoring of hydraulic fracture stimulation at the Habanero Enhanced Geothermal System, Cooper Basin, South Australia

Magnetotelluric (MT) data were collected across the Habanero Enhanced Geothermal System project in the Cooper Basin, South Australia. A baseline regional MT survey consisting of two profiles was collected to delineate the pre-injection resistivity structure. Two dimensional inversions of the MT data reveal three main resistivity structures to a depth of 5 km. The low resistivity surface layer (about 1.5 km thick) is interpreted as poorly consolidated sediments of Lake Eyre and Eromanga Basins. Below the conductive layer, a zone with relatively high resistivity with thickness of 2 km can be correlated to consolidated Cooper Basin sediments. A high resistivity zone below depths of 3.5 km is interpreted as the hot intrusive granodiorite (granite) of the Big Lake Suite with low porosity and permeability. This deep structure is also related to the Habanero EGS reservoir. The second MT survey was conducted during stimulation of Habanero-4 well by Geodynamics Ltd, where 36.5 ML of water with a resistivity of 13 Ωm (at 25°C) was injected at a relatively continuous rate of between 27–53 L/s over 14 days at a depth of almost 4 km. Analysis of pre- and post-injection residual phase tensors for periods greater than 10 s indicate conductive fractures oriented in a N/NNE direction. Apparent resistivity maps also revealed that injected fluids possibly propagated towards N/NNE direction. This result is in agreement with the micro-seismic events with an area of 4 km2 observed during fluid injection, as well as orientation of pre-existing N-S striking sub-horizontal fractures susceptible to slip due to stimulation. The MT responses close to injection show on average 5% decrease in apparent resistivity at periods greater than 10 s. The main reasons for observing subtle changes in resistivity at Habanero EGS is the screening effect of the conductive thick sedimentary cover (about 3.6 km thick) and the presence of pre-existing saline fluids with resistivity of 0.1 Ωm (equivalent to salinity of 16.1 g/L at 240°C) in the natural fractures. Overall, the MT monitoring at Habanero EGS highlights the need for favourable geological settings to measure significant changes in resistivity in EGS reservoirs.

Large scale magnetotelluric sounding at the periphery of the Songliao Basin, NE China

Recently, China Geological Survey (CGS) has launched 3D geological mapping programs from regional to local scales. The project Deep geological survey at the periphery of the Songliao Basin funded by CGS was implemented from 2012 to 2014. Its main goals are to reveal the tectonic framework of the Jarud Basin (JB) as well as to identify the strata distribution of Permian Linxi Formation by integrating new electromagnetic data with existing geophysical and geological data since black mudstones in the Linxi Formation have shown the potential of shale gas. The study area is situated in Jarud Banner and Ar Horqin Banner, Inner Mongolia, China. It is covered dominantly with Cretaceous-Jurassic igneous rocks with exception of the small southeastern part. It is tectonically located in the southern Great Khingan Range, western margin of the Songliao Basin, north of Xar Moron Fault. Over years of 2012 to 2014, a magnetotelluric survey was carried out at the west of the Songliao Basin. A total of 1559 stations including existing MT data on eight NW and five NE profiles were obtained, covering area that exceeds 10,000 km2. After dimensionality analysis and static shift removal, the nonlinear conjugate algorithm was used to conduct 2D inversion for TM and TE modes. Inversion results revealed numerous large faults, some of which constitute the boundaries of the Jarud Basin, and modified the tectonic framework. Integrated with well logging and geological data, two Paleozoic fault depressions (Gadasu and Hunnitu) and one Mesozoic depression was discovered. Two Paleozoic sag were inferred to be presence of Linxi Fms. One Mesozoic sag was inferred to be hydrocarbon potential. Attention should be paid to Gadasu sag with area of around 500 km2 since it contains reasonably thick conductive sediments exceeding 4 km in depth which might be black mudstones pertaining to shale gas.

Magnetotelluric monitoring of permeability enhancement at enhanced geothermal system project

Magnetotelluric (MT) data were collected across the Habanero Enhanced Geothermal System (EGS) project in the Cooper Basin, South Australia. A baseline regional MT survey consisting of two profiles were collected to delineate subsurface resistivity structure. An MT monitoring survey was conducted during stimulation of the Habanero-4 well. Inversions of the MT data in 2-D reveal three main resistivity layers to a depth of 5km. The surface layer is ≤6Ωm, 1.5km thick, and composed of poorly consolidated sediments of Lake Eyre and Eromanga Basins. The second layer is ≤25Ωm, 2km thick, and correlated to consolidated Cooper Basin sediments. A high resistivity zone below depths of 3.5km is interpreted as the hot intrusive granodiorite of the Big Lake Suite related to the Habanero EGS reservoir. The second MT survey was conducted during stimulation of Habanero-4, where 36.5 million liters (ML) of water with a resistivity of 13Ωm was injected over 14days. Analysis of pre- and post-injection residual phase tensors show possible conductive fractures oriented in a N-S direction for periods greater than 10s. Apparent resistivity maps also revealed that injected fluids possibly propagated towards N-S direction. This result is in agreement with micro-seismic events observed at the Habanero EGS during fluid injection. The MT responses close to injection show on average 5% decrease in apparent resistivity for periods greater than 10s. The main reasons for observing subtle changes in resistivity at Habanero EGS is the screening effect of the conductive thick sedimentary cover. Analysis of time-lapse models indicate an increase in total conductance of about 25S in the N-S direction, which likely indicate anisotropic permeability generated by hydraulic stimulation. Overall, the MT monitoring at Habanero EGS highlights the need for favorable geological settings and/or controlled source and downhole EM methods to measure significant changes in resistivity in EGS reservoirs.