A magnetotelluric (MT) survey has been performed in Gediz Graben located in western Turkey. The m... more A magnetotelluric (MT) survey has been performed in Gediz Graben located in western Turkey. The main goal of the survey is to search for additional geothermal sources to enlarge the city heating system. Three-dimensional (3D) inversion of the full impedance tensor provides valuable information on the current reservoir situation and reveals that it has no extra capacity for new subscribers. However, the low resistivity anomalies in the deeper part of the graben sedimentary fillings is probably related to clay alteration zones caused by hydrothermal activities. The hot fluids outflow along the cracks and fractures of normal faults presence in the study area. Interpretation of the 3D resistivity model suggests that the extension of normal faults in the metamorphic basement can be considered as a promising reservoir zones.
Thanks to the active development of numerical algorithms in the EM community, three dimensional (... more Thanks to the active development of numerical algorithms in the EM community, three dimensional (3D) electromagnetic modelling and inversion methods have been successfully applied to a wide range of geophysical problems at a range of scales, from the investigation of groundwater to the study of continental tectonics (e.g. [Cox et al., 2010; Schwarzbach et al., 2011; Murphy and Egbert, 2017]). However, widely available inversion programs such as ModEM or WSINV3DMT are not able to make effective use of advances in computer hardware and supercomputing technology over the last decade, imposing severe restrictions on grid resolution, and limiting our ability to explore model space. Here we discuss our recent efforts to implement scalable massively parallel computational approaches in the ModEM software.
10th Congress of the Balkan Geophysical Society, 2019
Summary A magnetotelluric survey has been conducted in the Cappadocia region of central Turkey in... more Summary A magnetotelluric survey has been conducted in the Cappadocia region of central Turkey in order to find new geothermal resources. The survey area has formerly been postulated as the location of a buried caldera that was one of the main eruptive centres of Cappadocian Volcanic Province. Three-dimensional non-linear conjugate gradient inversion of magnetotelluric data by using the full impedance tensor helps to delineate the subsurface resistivity distribution. The derived resistivity model reveals the possibility of a buried caldera. The low resistivity anomalies are interpreted as the clay alteration zones caused by hydrothermal activities.
The electrical resistivity tomography (ERT) method provides moderately good constraints for both ... more The electrical resistivity tomography (ERT) method provides moderately good constraints for both conductive and resistive structures, while the radio-magnetotelluric (RMT) method is well suited to constrain conductive structures. Additionally, RMT and ERT data may have different target coverage and are differently affected by various types of noise. Hence, joint inversion of RMT and ERT data sets may provide a better constrained model as compared to individual inversions. In this study, joint inversion of boat-towed RMT and lake-floor ERT data has for the first time been formulated and implemented. The implementation was tested on both synthetic and field data sets incorporating RMT transverse electrical mode and ERT data. Results from synthetic data demonstrate that the joint inversion yields models with better resolution compared with individual inversions. A case study from an area adjacent to thë Aspö Hard Rock Laboratory (HRL) in southeastern Sweden was used to demonstrate the implementation of the method. A 790-m-long profile comprising lake-floor ERT and boattowed RMT data combined with partial land data was used for this purpose. Joint inversions with and without weighting (applied to different data sets, vertical and horizontal model smoothness) as well as constrained joint inversions incorporating bathymetry data and water resistivity measurements were performed. The resulting models delineate subsurface structures such as a major northeasterly directed fracture system, which is observed in the HRL facility underground and confirmed by boreholes. A previously uncertain weakness zone, likely a fracture system in the northern part of the profile, is inferred in this study. The fractures are highly saturated with saline water, which make them good targets of resistivity-based geophysical methods. Nevertheless, conductive sediments overlain by the lake water add further difficulty to resolve these deep fracture zones. Therefore, the joint inversion of RMT and ERT data particularly helps to improve the resolution of the resistivity models in areas where the profile traverses shallow water and land sections. Our modification of the joint inversion of RMT and ERT data improves the study of geological units underneath shallow water bodies where underground infrastructures are planned. Thus, it allows better planning and mitigating the risks and costs associated with conductive weakness zones.
We analyzed the 3-D resistivity structure beneath Naruko volcano, northeastern Japan, with the ai... more We analyzed the 3-D resistivity structure beneath Naruko volcano, northeastern Japan, with the aim of imaging 3-D distribution of fluids in the crust for its volcanic and seismogenic implications. The data were recorded at 77 sites in total: 30 sites are new and are arranged in an approximately 5 × 5 km grid whereas the remaining older sites constitute two separate east-west profiles. We ran a 3-D inversion using full components of impedance tensors in the period range between 0.13 and 400 s. The resulting model showed that a sub-vertical conductor exists a few kilometers below Naruko volcano. The conductor extends from the surface of the volcano and dips towards the south, away from the volcano towards the backbone range. High levels of seismicity are observed in the upper crust above and around the conductors. We suggest that the seismicity is fluid driven and that a fluid trap is created by the precipitation of quartz owing to a reduction in solubility at shallow depth. The Quaternary volcanic front is characterized by a sharp resistivity contrast and a high-resistivity zone and extends 10 to 15 km towards the east. A fore-arc conductor was observed at mid-crustal levels even farther towards the east. The sub-vertical conductors along the arc and the fore-arc conductor have resistivities of 1 to 10 Ωm. Assuming a Hashin-Shtrikman model with saline fluids of 0.1-Ωm resistivity, a porosity of 1.5% to 15% is required to explain the observed conductive anomalies.
Fault zones are the locations where motion of tectonic plates, often associated with earthquakes,... more Fault zones are the locations where motion of tectonic plates, often associated with earthquakes, is accommodated. Despite a rapid increase in the understanding of faults in the last decades, our knowledge of their geometry, petrophysical properties, and controlling processes remains incomplete. The central questions addressed here in our study of the Dead Sea Transform (DST) in the Middle East are as follows: (1) What are the structure and kinematics of a large fault zone? (2) What controls its structure and kinematics? (3) How does the DST compare to other plate boundary fault zones? The DST has accommodated a total of 105 km of left-lateral transform motion between the African and Arabian plates since early Miocene ($20 Ma). The DST segment between the Dead Sea and the Red Sea, called the Arava/Araba Fault (AF), is studied here using a multidisciplinary and multiscale approach from the mm to the plate tectonic scale. We observe that under the DST a 35 narrow, subvertical zone cuts through crust and lithosphere. 36 First, from west to east the crustal thickness increases 37 smoothly from 26 to 39 km, and a subhorizontal lower 38 crustal reflector is detected east of the AF. Second, several 39 faults exist in the upper crust in a 40 km wide zone centered 40 on the AF, but none have kilometer-size zones of decreased 41 seismic velocities or zones of high electrical conductivities 42 in the upper crust expected for large damage zones. Third, 43 the AF is the main branch of the DST system, even though it 44 has accommodated only a part (up to 60 km) of the overall 45 105 km of sinistral plate motion. Fourth, the AF acts as a 46 barrier to fluids to a depth of 4 km, and the lithology 47 changes abruptly across it. Fifth, in the top few hundred 48 meters of the AF a locally transpressional regime is 49 observed in a 100-300 m wide zone of deformed and 50 displaced material, bordered by subparallel faults forming a 51 positive flower structure. Other segments of the AF have a
We have performed a set of three dimensional inversions of magnetotelluric data in the Snake Rive... more We have performed a set of three dimensional inversions of magnetotelluric data in the Snake River Plain and Yellowstone areas. We used a total of 73 sites from USArray MT Transportable Array (Idaho, Montana and Wyoming areas) and a subset of 19 sites from an earlier long-period MT survey in the Snake River Plain (SRP). Data for 14 periods from 7.3 secs to 5.2 hours were inverted for 3D inverse conductivity models on 7 and 14 km grids, fitting both the impedances (with 5% error floors) and the vertical magnetic transfer ...
2011 GSA Annual Meeting in Minneapolis, Oct 11, 2011
In the past six years, EarthScope MT (EMscope) transportable array has covered much of western Un... more In the past six years, EarthScope MT (EMscope) transportable array has covered much of western United States, extending from the US-Canadian border in the North, to Northern California, Nevada and Utah in the South on a quasi-regular grid with 70 km nominal resolution. After 2011, the focus of EMscope moves to the mid-continent rift.
Long period (10-20,000 s) magnetotelluric (MT) data are being acquired in a series of temporary a... more Long period (10-20,000 s) magnetotelluric (MT) data are being acquired in a series of temporary arrays deployed across the continental United States through the EMScope component of EarthScope. MT deployments in 2006-2011 have acquired data at 325 sites on an approximately regular grid, with the same nominal spacing as the USArray broadband seismic transportable array (~ 70 km). The MT sites span a rectangular area from NW Washington to NW Colorado. Here we present results of a 3-D inversion of the full data set ...
We have performed a set of three dimensional inversions of magnetotelluric data in the Snake Rive... more We have performed a set of three dimensional inversions of magnetotelluric data in the Snake River Plain and Yellowstone areas. We used a total of 73 sites from Earthscope MT Transportable Array (Idaho, Montana and Wyoming areas) and a subset of 19 sites from an earlier long-period MT survey in the Snake River Plain (SRP). Data for 14 periods from 7.3 secs to 5.2 hours were inverted for 3D inverse conductivity models on 7 and 14 km grids, fitting both the impedances (with 5% error floors) and the vertical magnetic transfer ...
A magnetotelluric (MT) survey has been performed in Gediz Graben located in western Turkey. The m... more A magnetotelluric (MT) survey has been performed in Gediz Graben located in western Turkey. The main goal of the survey is to search for additional geothermal sources to enlarge the city heating system. Three-dimensional (3D) inversion of the full impedance tensor provides valuable information on the current reservoir situation and reveals that it has no extra capacity for new subscribers. However, the low resistivity anomalies in the deeper part of the graben sedimentary fillings is probably related to clay alteration zones caused by hydrothermal activities. The hot fluids outflow along the cracks and fractures of normal faults presence in the study area. Interpretation of the 3D resistivity model suggests that the extension of normal faults in the metamorphic basement can be considered as a promising reservoir zones.
Thanks to the active development of numerical algorithms in the EM community, three dimensional (... more Thanks to the active development of numerical algorithms in the EM community, three dimensional (3D) electromagnetic modelling and inversion methods have been successfully applied to a wide range of geophysical problems at a range of scales, from the investigation of groundwater to the study of continental tectonics (e.g. [Cox et al., 2010; Schwarzbach et al., 2011; Murphy and Egbert, 2017]). However, widely available inversion programs such as ModEM or WSINV3DMT are not able to make effective use of advances in computer hardware and supercomputing technology over the last decade, imposing severe restrictions on grid resolution, and limiting our ability to explore model space. Here we discuss our recent efforts to implement scalable massively parallel computational approaches in the ModEM software.
10th Congress of the Balkan Geophysical Society, 2019
Summary A magnetotelluric survey has been conducted in the Cappadocia region of central Turkey in... more Summary A magnetotelluric survey has been conducted in the Cappadocia region of central Turkey in order to find new geothermal resources. The survey area has formerly been postulated as the location of a buried caldera that was one of the main eruptive centres of Cappadocian Volcanic Province. Three-dimensional non-linear conjugate gradient inversion of magnetotelluric data by using the full impedance tensor helps to delineate the subsurface resistivity distribution. The derived resistivity model reveals the possibility of a buried caldera. The low resistivity anomalies are interpreted as the clay alteration zones caused by hydrothermal activities.
The electrical resistivity tomography (ERT) method provides moderately good constraints for both ... more The electrical resistivity tomography (ERT) method provides moderately good constraints for both conductive and resistive structures, while the radio-magnetotelluric (RMT) method is well suited to constrain conductive structures. Additionally, RMT and ERT data may have different target coverage and are differently affected by various types of noise. Hence, joint inversion of RMT and ERT data sets may provide a better constrained model as compared to individual inversions. In this study, joint inversion of boat-towed RMT and lake-floor ERT data has for the first time been formulated and implemented. The implementation was tested on both synthetic and field data sets incorporating RMT transverse electrical mode and ERT data. Results from synthetic data demonstrate that the joint inversion yields models with better resolution compared with individual inversions. A case study from an area adjacent to thë Aspö Hard Rock Laboratory (HRL) in southeastern Sweden was used to demonstrate the implementation of the method. A 790-m-long profile comprising lake-floor ERT and boattowed RMT data combined with partial land data was used for this purpose. Joint inversions with and without weighting (applied to different data sets, vertical and horizontal model smoothness) as well as constrained joint inversions incorporating bathymetry data and water resistivity measurements were performed. The resulting models delineate subsurface structures such as a major northeasterly directed fracture system, which is observed in the HRL facility underground and confirmed by boreholes. A previously uncertain weakness zone, likely a fracture system in the northern part of the profile, is inferred in this study. The fractures are highly saturated with saline water, which make them good targets of resistivity-based geophysical methods. Nevertheless, conductive sediments overlain by the lake water add further difficulty to resolve these deep fracture zones. Therefore, the joint inversion of RMT and ERT data particularly helps to improve the resolution of the resistivity models in areas where the profile traverses shallow water and land sections. Our modification of the joint inversion of RMT and ERT data improves the study of geological units underneath shallow water bodies where underground infrastructures are planned. Thus, it allows better planning and mitigating the risks and costs associated with conductive weakness zones.
We analyzed the 3-D resistivity structure beneath Naruko volcano, northeastern Japan, with the ai... more We analyzed the 3-D resistivity structure beneath Naruko volcano, northeastern Japan, with the aim of imaging 3-D distribution of fluids in the crust for its volcanic and seismogenic implications. The data were recorded at 77 sites in total: 30 sites are new and are arranged in an approximately 5 × 5 km grid whereas the remaining older sites constitute two separate east-west profiles. We ran a 3-D inversion using full components of impedance tensors in the period range between 0.13 and 400 s. The resulting model showed that a sub-vertical conductor exists a few kilometers below Naruko volcano. The conductor extends from the surface of the volcano and dips towards the south, away from the volcano towards the backbone range. High levels of seismicity are observed in the upper crust above and around the conductors. We suggest that the seismicity is fluid driven and that a fluid trap is created by the precipitation of quartz owing to a reduction in solubility at shallow depth. The Quaternary volcanic front is characterized by a sharp resistivity contrast and a high-resistivity zone and extends 10 to 15 km towards the east. A fore-arc conductor was observed at mid-crustal levels even farther towards the east. The sub-vertical conductors along the arc and the fore-arc conductor have resistivities of 1 to 10 Ωm. Assuming a Hashin-Shtrikman model with saline fluids of 0.1-Ωm resistivity, a porosity of 1.5% to 15% is required to explain the observed conductive anomalies.
Fault zones are the locations where motion of tectonic plates, often associated with earthquakes,... more Fault zones are the locations where motion of tectonic plates, often associated with earthquakes, is accommodated. Despite a rapid increase in the understanding of faults in the last decades, our knowledge of their geometry, petrophysical properties, and controlling processes remains incomplete. The central questions addressed here in our study of the Dead Sea Transform (DST) in the Middle East are as follows: (1) What are the structure and kinematics of a large fault zone? (2) What controls its structure and kinematics? (3) How does the DST compare to other plate boundary fault zones? The DST has accommodated a total of 105 km of left-lateral transform motion between the African and Arabian plates since early Miocene ($20 Ma). The DST segment between the Dead Sea and the Red Sea, called the Arava/Araba Fault (AF), is studied here using a multidisciplinary and multiscale approach from the mm to the plate tectonic scale. We observe that under the DST a 35 narrow, subvertical zone cuts through crust and lithosphere. 36 First, from west to east the crustal thickness increases 37 smoothly from 26 to 39 km, and a subhorizontal lower 38 crustal reflector is detected east of the AF. Second, several 39 faults exist in the upper crust in a 40 km wide zone centered 40 on the AF, but none have kilometer-size zones of decreased 41 seismic velocities or zones of high electrical conductivities 42 in the upper crust expected for large damage zones. Third, 43 the AF is the main branch of the DST system, even though it 44 has accommodated only a part (up to 60 km) of the overall 45 105 km of sinistral plate motion. Fourth, the AF acts as a 46 barrier to fluids to a depth of 4 km, and the lithology 47 changes abruptly across it. Fifth, in the top few hundred 48 meters of the AF a locally transpressional regime is 49 observed in a 100-300 m wide zone of deformed and 50 displaced material, bordered by subparallel faults forming a 51 positive flower structure. Other segments of the AF have a
We have performed a set of three dimensional inversions of magnetotelluric data in the Snake Rive... more We have performed a set of three dimensional inversions of magnetotelluric data in the Snake River Plain and Yellowstone areas. We used a total of 73 sites from USArray MT Transportable Array (Idaho, Montana and Wyoming areas) and a subset of 19 sites from an earlier long-period MT survey in the Snake River Plain (SRP). Data for 14 periods from 7.3 secs to 5.2 hours were inverted for 3D inverse conductivity models on 7 and 14 km grids, fitting both the impedances (with 5% error floors) and the vertical magnetic transfer ...
2011 GSA Annual Meeting in Minneapolis, Oct 11, 2011
In the past six years, EarthScope MT (EMscope) transportable array has covered much of western Un... more In the past six years, EarthScope MT (EMscope) transportable array has covered much of western United States, extending from the US-Canadian border in the North, to Northern California, Nevada and Utah in the South on a quasi-regular grid with 70 km nominal resolution. After 2011, the focus of EMscope moves to the mid-continent rift.
Long period (10-20,000 s) magnetotelluric (MT) data are being acquired in a series of temporary a... more Long period (10-20,000 s) magnetotelluric (MT) data are being acquired in a series of temporary arrays deployed across the continental United States through the EMScope component of EarthScope. MT deployments in 2006-2011 have acquired data at 325 sites on an approximately regular grid, with the same nominal spacing as the USArray broadband seismic transportable array (~ 70 km). The MT sites span a rectangular area from NW Washington to NW Colorado. Here we present results of a 3-D inversion of the full data set ...
We have performed a set of three dimensional inversions of magnetotelluric data in the Snake Rive... more We have performed a set of three dimensional inversions of magnetotelluric data in the Snake River Plain and Yellowstone areas. We used a total of 73 sites from Earthscope MT Transportable Array (Idaho, Montana and Wyoming areas) and a subset of 19 sites from an earlier long-period MT survey in the Snake River Plain (SRP). Data for 14 periods from 7.3 secs to 5.2 hours were inverted for 3D inverse conductivity models on 7 and 14 km grids, fitting both the impedances (with 5% error floors) and the vertical magnetic transfer ...
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