EMRP2.12 | Electromagnetic Induction in Geophysics: Data, Models, Inversions and Interpretations
EDI
Electromagnetic Induction in Geophysics: Data, Models, Inversions and Interpretations
Convener: Duygu Kiyan | Co-conveners: Shunguo Wang, Paula Rulff, Pierre WAWRZYNIAK
Orals
| Thu, 27 Apr, 16:15–17:50 (CEST)
 
Room -2.21, Fri, 28 Apr, 08:30–09:50 (CEST)
 
Room -2.21
Posters on site
| Attendance Wed, 26 Apr, 16:15–18:00 (CEST)
 
Hall X2
Orals |
Thu, 16:15
Wed, 16:15
This session asks for contributions in the field of electromagnetic (EM) geophysical methods that are applied on various scales ranging from the near-surface to the deep mantle. This includes new instrumentation and data acquisition methods, as well as mathematical and numerical improvements to data processing, modelling, and inversion applied to ground-based and off-shore measurements, airborne and satellite missions. We are interested in studies of EM applied to global induction, imaging regional scale tectonic, magmatic, or volcanic systems, in the search for hydrocarbon, geothermal, or mineral resources, and the investigation of near surface structure relevant to environmental, urban, and hydrological systems. Results from EM methods are often part of multi-disciplinary studies integrating data from rock physics and other geophysical, geochemical, and geological methods to investigate complex subsurface structures and their temporal evolution. Neighbouring fields of research encompass the study of natural and controlled EM sources, geo-magnetically induced currents, space weather, or geomagnetic field studies based on observatory data.

Orals: Thu, 27 Apr | Room -2.21

Chairpersons: Shunguo Wang, Paula Rulff, Duygu Kiyan
16:15–16:20
16:20–16:40
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EGU23-6068
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solicited
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On-site presentation
Max Moorkamp

The tectonic history of southern Africa includes Archean craton formation, multiple episodes of subduction and rifting and some of the world's most significant magmatic events. Lithospheric models based on seismological and magnetotelluric data show highly heterogeneous crustal structure, significant anomalies in the lithospheric mantle and strong variations of the depth to the lithosphere-asthenosphere boundary. While some of the spatial patterns agree between different geophysical methods, there are also significant differences in the geometry and location of many structures. I perform a joint inversion of magnetotelluric and satellite gravity data to reconcile these apparent discrepancies. Resistivity and density are coupled through a newly developed Variation of Information constraint which strives to establish a one-to-one relationship between the two quantities. This allows the resistivity-density relationship to evolve data driven during the inversion. The final combined resistivity-density model shows detailed lithospheric and sub-lithospheric structure below the Kaapvaal Craton and adjacent mobile belts. In addition, the retrieved parameter relationship exhibits several branches indicating strong variations in composition. Compared to results from a similar inversion in the western United States, the inversion indicates significantly less fluid related low resistivity anomalies and a dominance of high-density low-resistivity structures. This corroborates earlier ideas that fluids are difficult to contain within in the Earth over long time scales. I will discuss the implications for the tectonic evolution of the region and for the interpretation of low resistivity anomalies world-wide.

How to cite: Moorkamp, M.: An integrated resistivity-density model of Southern Africa, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6068, https://doi.org/10.5194/egusphere-egu23-6068, 2023.

16:40–16:50
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EGU23-10193
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ECS
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On-site presentation
Mitra Kangazian and Colin Farquharson

Minimum-structure, or Occam’s, style of inversion deals with the fundamental non-uniqueness of the inverse problem by finding the simplest Earth model that reproduces the observations. As an additional consequence of this approach, minimum-structure inversion is also reliable and robust. Because of these reasons, it has been extensively utilized in mineral and petroleum exploration problems, and lithospheric studies. The method has been adapted and extended in many ways to obtain more reliable and realistic models of the Earth’s subsurface. Joint inversion of geophysical data-sets is one of the most important extensions of minimum-structure inversion. This method can reduce the non-uniqueness of the inverse problem by combing two, or more, different geophysical data-sets in a single inverse problem. Different geophysical methods have different sensitivity to different physical properties, hence, it is hoped that the null space for one type of data can be spanned by the other.

Joint inversion algorithms can be divided into two main categories, structural-based and petrophysical-based joint inversion methods, depending on the coupling measure used between the physical property models. We have adopted the fuzzy c-mean (FCM) clustering technique which is a petrophysical-based method to jointly invert MT and gravity data-sets. The optimization of this method is not as challenging as for structural-based approaches. We have also performed constrained FCM clustering for independent MT and gravity inversions to compare the constructed models of this method with the joint inversion, and independent MT and gravity inversions. The FCM clustering method makes effective use of statistical petrophysical data which may exist in complex geological structures, or can be anticipated, to encourage the inverted physical property values to move towards the a priori petrophysical data as target clusters.

The capabilities of the joint and constrained FCM clustering inversion are evaluated on synthetic and real examples. The constructed density and conductivity models from the joint inversion have a more plausible representation of the true model’s geometry and have a reasonable range of the recovered physical property values compared to the independent constrained FCM clustering technique and independent unconstrained MT and gravity inversions.

Keywords: Fuzzy c-mean clustering, Gravity, Joint inverse problem, MT, Unstructured tetrahedral mesh

How to cite: Kangazian, M. and Farquharson, C.: Fuzzy c-mean clustering joint inversion of magnetotelluric (MT) and gravity data-sets using unstructured tetrahedral meshes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10193, https://doi.org/10.5194/egusphere-egu23-10193, 2023.

16:50–17:00
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EGU23-347
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ECS
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On-site presentation
Gokhan Karcioglu, Ersan Turkoglu, and Umit Avsar

The western part of the Anatolian peninsula is defined with an N-S extensional regime and resulting graben systems, referred as the Aegean Extensional Province (AEP). The transition of this extensional regime in the west to E-W compressional regime in the east is bounded by the Isparta Angle, which is a reverse v-shaped major structure developed due to nappe emplacements and related clockwise and counter-clockwise rotations.

The study area is located at the eastern end of the Curuksu Graben and covers the western part of the Acigol Graben. Curuksu Graben is part of the Denizli Horst-Graben system and located between the junction point of three major grabens of the AEP in the west and Acigol Graben in the east. The development of the Graben systems in the AEP, including Curuksu and Acigol grabens, is resulted from two extensional periods interrupted by a compressional phase creating a disconformity between deformed ancient and undeformed neotectonic graben fills in the region. Denizli Horst-Graben System consists of incipient grabens and the modern graben (Curuksu Graben) which is developed with the introduction of the neotectonic regime with the latest Pliocene. This episodic development caused an inward development of normal faults. The compressional regime created many strike-slip and reverse faults in the region while many of the currently active normal faults with strike-slip components are resulted from the present day NNE-SSW extensional phase, including seismically active margin-bounding major faults with seismic hazard potential.

In this study, we have reassessed the data from 300 Magnetotelluric stations which were previously collected by a private contractor for geothermal research purposes. We have investigated the main properties of the data with Phase Tensor analysis and inverted it using ModEM software to reveal 3D subsurface conductivity structure of the area. Our analysis shows that the Phase Tensor ellipses for the highest frequencies indicate rather 1D behavior in compliance with the undeformed, nearly horizontal bedding of the neotectonic graben fills. The strike directions obtained through induction vectors and Phase Tensor ellipses reflects the dominant effect of the major faults and conductive basin fills. The recovered model from the 3D inversion results show the depth of the basin fills and conductivity anomalies due to normal faults controlling the basin development.

How to cite: Karcioglu, G., Turkoglu, E., and Avsar, U.: Resistivity structure of Denizli Çürüksu & Acıgöl Graben connection: Preliminary results from 3D inversion of magnetotelluric data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-347, https://doi.org/10.5194/egusphere-egu23-347, 2023.

17:00–17:10
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EGU23-16800
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On-site presentation
M. Emin Candansayar, İsmail Demirci, N. Yıldırım Gündoğdu, M.Doğukan Oskay, and Erhan Erdoğan

We collected long-period magnetotelluric (LMT) data on the 64 stations by using a remotely controlled measurement system in northwestern Anatolia, Türkiye. The data was collected along four nearly parallel 300-km-long lines. In our previous project, we already collected broadband magnetotelluric(MT) data on 358 stations along those four lines. These lines are crossing main tectonic traverses such as North Anatolia Fault Zones, and Intra-Pontid Suture zones.  The remotely controlled MT measurement system provides us to control data quality during measurement and we can change the station location if the data quality is not good in the current stations.  This ensures the good data quality of all MT sites. After the time series analysis and main data processing procedure such as phase tensor decomposition and static shift correction, we interpreted each line's data set by using a two-dimensional inversion algorithm. We also inverted LMT data by using a three-dimensional inversion algorithm. The three-dimensional resistivity model also showed us to main tectonic units as two-dimensional resistivity models. Additionally, crust lithosphere relations were also revealed. We obtained upper and lower crust boundaries by using magnetic data and crust al depth by using gravity data. Those results also validated our resistivity models obtained from MT data inversion. We are going to give preliminary interpretation results of the lithosphere structure of northwest Anatolia in this presentation.

Acknowledgement:  This study is supported by TUBITAK (The Scientific and Technological Research Council of Turkey) Project with Grant Number 119Y197. We thanks TUBITAK.

How to cite: Candansayar, M. E., Demirci, İ., Gündoğdu, N. Y., Oskay, M. D., and Erdoğan, E.: Revealing Lithospheric structure of Northwestern Anatolia by using 3D inversion of Long Period Magnetotelluric Data collected remotely controlled measurement system: Preliminary results, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16800, https://doi.org/10.5194/egusphere-egu23-16800, 2023.

17:10–17:20
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EGU23-7983
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ECS
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On-site presentation
Ji’en Dong and Gaofeng Ye*

The South China Block (SCB) is located at the junction of the Pacific, Eurasian, and Tethys plates. Their interaction led to large-scale multi-stage mineralization in the SCB during the Mesozoic. Several regional ore-concentration areas, such as the Middle-Lower Yangtze metallogenic belt (MLYMB), the Wuyishan metallogenic belt (WYMB), the Nanling metallogenic belt (NLMB), and the Qinzhou-Hangzhou Metallogenic Belt (QHMB) were formed during this process. However, the mineral types of these metallogenic belts are different. To study the deep mechanisms of the different metallogenic types developed in the same tectonic background at almost the same period, the magnetotelluric sounding (MT) data from 691 sites located mainly within the eastern SCB (Fig.1) are employed to obtain a regional lithospheric 3-D resistivity model.

According to this model, Large-scale low-resistivity bodies extend from the crust to the upper mantle beneath the MLYMB and the QHMB, which are interpreted as channels of upper mantle upwelling. While the upper- to mid-crust beneath the WYMB and the NLMB is characterized by high resistivity with small-scale low-resistivity anomalies, indicating upwelling mantle materials having invaded the crust on a small scale. Large-scale upper mantle low-resistivity anomalies extend along its strike direction beneath the MLYMB and the QHMB. It could be concluded from the resistivity model that deep low-resistivity anomalies and mantle upwelling channels mainly controlled almost all the Mesozoic deposits(Fig.3). However, the scales of low-resistivity anomalies and upper-crust ore-controlling structures are different. Significantly, the upper-mantle low-resistivity anomalies beneath the eastern SCB show a spatial distribution that is gradually shallowing from south to north, probably indicating that the asthenospheric materials are upwelling from south to north, corresponding with the changing progressively of magma and metallogenic activities. We propose that the lithospheric delamination and asthenospheric upwelling caused by the far-field effects of the paleo-Pacific Plate subduction are the source of solid magmatic activities and related metallogeny (Fig.3).

* This work was jointly supported by the China Geological Survey project (DD20160082 and DD20190012) and the SINOPROBE project.

Fig. 1 Distribution of MT stations within the study area. The metallogenic belts after Yan et al. (2021).

Fig.2 Horizontal slices of 3-D resistivity model. Deposit data after Mao et al. (2018).

 Fig.3 A comprehensive 3-D diagram illustrating the possible formation mechanism of the metallogenic belts.

References

Mao, J., Xie, G., Yuan, S., Liu, P., Meng, X., Zhou, Z., & Zheng, W. (2018). Current research progress and future trends of porphyry-skarn copper and granite-related tin polymetallic deposits in the Circum Pacific metallogenic belts. Acta Petrologica Sinica, 34(9), 3-19.

Yan, J., Lü, Q., Luo, F., Cheng, S., Zhang, K., Zhang, Y., et al. (2021). A gravity and magnetic study of lithospheric architecture and structures of South China with implications for the distribution of plutons and mineral systems of the main metallogenic belts. Journal of Asian Earth Sciences, 221, 104938.

 

How to cite: Dong, J. and Ye*, G.: Relationship between electrical conductivity, metallogeny, and lithospheric structure in South China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7983, https://doi.org/10.5194/egusphere-egu23-7983, 2023.

17:20–17:30
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EGU23-12387
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On-site presentation
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Matthew Joseph Comeau, Graham J. Hill, Svetlana Kovacikova, Jochen Kamm, Réka Lukács, Ioan Seghedi, and Harangi Szabolcs

Ciomadul volcano, located at the south-eastern terminus of the Carpathian volcanic arc (Romania), is the youngest volcano in eastern-central Europe, with the last eruption occurring at 32 ka. Petrological and geophysical constraints indicate a melt-bearing silicic crystal mush body beneath Ciomadul, approximately 5–20 km below surface. This suggests that long-dormant or seemingly inactive volcanoes may have potentially active magma storage systems. However, the geometry and size of the magma storage region is unknown. Understanding the nature and structure of the volcanic plumbing system is crucial to understanding the evolution of the system, as well as to assess the hazard potential.

In this presentation, we will report on 41 new magnetotelluric measurements acquired in 2022. The survey design consists of an irregular grid with dimensions of approximately 75 km by 75 km, centered around Ciomadul in the corner of the south-eastern Carpathian Mountains. This makes an array suitable for three-dimensional modelling. A 100 km long NW-SE transect across the array has a measurement spacing of less than 15 km.

The newly acquired data complement previous measurements (recorded in 2010) near Ciomadul and Băile Tuşnad within an area of approximately 5 km by 10 km. The new data extend westward to the Perşani volcanic field (Racoș, Homorod), about 40 km west of Ciomadul, towards the Transylvanian Basin, and to the south-east to the edge of the seismically active Vrancea zone, often attributed to the descent of a slab, more than 50 km south-east of Ciomadul, towards the Focșani Basin. Both regions are targets for future measurement campaigns.

Recordings were carried out at each location for approximately 1–5 days. The data typically had reliable periods of up to 1,000–4,000 s. The data are not homogenous and have characteristics of three-dimensionality. At some locations, cultural electromagnetic noise contaminated the signals and degraded the data; thus choosing appropriate locations for measurement was critical. Estimating local and inter-station transfer functions required special care, such as applying data pre-selection schemes and manual time windows, in addition to standard approaches including using robust statistics and the remote reference method. Overall, the preliminary analysis is encouraging and the results show that it is possible to obtain usable magnetotelluric data in this region.

How to cite: Comeau, M. J., Hill, G. J., Kovacikova, S., Kamm, J., Lukács, R., Seghedi, I., and Szabolcs, H.: Magnetotelluric data across Ciomadul volcano and the Perşani Volcanic Field — constrains on the nature and structure of the magma storage system, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12387, https://doi.org/10.5194/egusphere-egu23-12387, 2023.

17:30–17:40
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EGU23-8695
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On-site presentation
Alexey Kuvshinov, Mikhail Kruglyakov, and Manoj Nair

Directional drilling in the oil fields relies particularly on the "on-fly" measurements of the natural magnetic field (measurements while drilling; MWD); the MWD are eventually used to construct the well path. These measurements are the superposition of the signals from the internal (core and crustal),  external (ionospheric and magnetospheric) sources, and the noise from magnetic elements in the borehole assembly. The internal signals are mostly constant in time and accounted for through the Earth's internal field models. The signals of external origin give rise to diurnal and irregular spatiotemporal magnetic field variations observable in the MWD. One of the common ways to mitigate the effects of these variations in the MWD is to correct readings for the data from an adjacent land-based magnetic observatory/site. This method assumes that the land-based signals are similar to those at the seabed drilling site. This study shows that the sea level and seabed horizontal magnetic fields differ significantly in many oceanic regions. We made this inference from the global electromagnetic induction modelling of the magnetic field using realistic models of conducting Earth and time-varying external sources. To perform such modelling, we elaborated a numerical approach to calculate efficiently the spatiotemporal evolution of the magnetic field. Finally, we propose and validate a formalism allowing researchers to obtain trustworthy seabed signals using measurements at the adjacent land-based site and exploiting the modelling results, thus without needing additional measurements at the seabed site.

How to cite: Kuvshinov, A., Kruglyakov, M., and Nair, M.: A Proper Use of the Adjacent Land-Based Magnetic Field Data to Account for the Geomagnetic Disturbances During Offshore Directional Drilling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8695, https://doi.org/10.5194/egusphere-egu23-8695, 2023.

17:40–17:50
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EGU23-16326
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On-site presentation
Weerachai Sarakorn, Phongphan Mukwachi, and Samak Boonpan

In this study, the novel artificial neural network(ANN) called back-propagation multilayer perceptron (BP-MLP) algorithm with fully connected architecture is proposed to simulate and predict the apparent resistivity and impedance phase of 2-D Magnetotelluric forward modeling. The experiments of this algorithm are made on various benchmark models. The experimental results showed that the proposed neural network is efficient and provides accurate predictions with an average relative error of apparent resistivity and impedance phase less than 1% and 0.5%, respectively. The algorithm's feasibility suggests that the ANN approach provides excellent accuracy results and can be practically used for solving 2-D magnetotelluric modeling.

How to cite: Sarakorn, W., Mukwachi, P., and Boonpan, S.: Novel Back-Propagation Multilayer Perceptron Approach for 2-D Magnetotelluric Modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16326, https://doi.org/10.5194/egusphere-egu23-16326, 2023.

Orals: Fri, 28 Apr | Room -2.21

Chairpersons: Duygu Kiyan, Paula Rulff
08:30–08:40
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EGU23-11690
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ECS
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On-site presentation
Sihong Wu, Qinghua Huang, and Li Zhao

The airborne electromagnetic (AEM) method is a modern technique in geophysical surveys with the merits of terrain adaptability and acquisition efficiency, and can image the electrical structure of the Earth’s subsurface down to several hundred meters. AEM survey has been applied extensively in mineral exploration, groundwater monitoring, environment investigation and geological mapping. However, the expansion of survey area and spatial sampling bring about huge volumes of AEM data, which present a serious computational challenge for rapid AEM inversion. Inspired by Google’s neural machine translation system, we develop a fast inversion system guided by deep learning to translate AEM data directly into subsurface resistivity structures. Synthetic tests demonstrate that our proposed inversion system has strong noise robustness and can provide reliable inversion results much more efficiently than the conventional Gauss-Newton algorithm. In the field data application, our system obtains robust inversion results of more than 740,000 AEM soundings acquired by the U.S. Geological Survey from the Leach Lake Basin in California in seconds on a common PC. The inverted images coincide exactly with previous studies of the local geological environment and clearly outline the geometries of the lake, faults and surrounding mountains. Our inversion system can support near real-time underground subsurface imaging for AEM surveys and inject new vigor into resource exploration and tectonic studies.

How to cite: Wu, S., Huang, Q., and Zhao, L.: Near real-time subsurface structure imaging using airborne electromagnetic data based on deep learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11690, https://doi.org/10.5194/egusphere-egu23-11690, 2023.

08:40–08:50
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EGU23-17211
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ECS
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On-site presentation
Maria Carrizo, Evert Slob, and Dieter Werthmüller

Frequency domain electromagnetic induction (FDEM) sensors are used regularly to investigate near-surface electrical properties for diverse purposes.  FDEM instruments measure the coupling ratio between the secondary magnetic field induced in the ground and the primary magnetic field of the direct wave propagating from a transmitter through the air to the receiver coil, which is a complex ratio, where the real part is called in-phase part and the real part is called the out-of-phase or quadrature part. Usually, the quadrature  part of the data measurements is used to estimate the electrical conductivity of the shallow subsurface. In this study we show the outcome of the estimation of an electrical conductivity model using both quadrature and in-phase  parts of the coupling ratio. We simulate the full solution measurements (quadrature and in-phase) and used only the quadrature part as data to estimate 1D electrical conductivity models of the subsurface in a lookup table. Then, we compare this estimation with the resulting one using the full solution as data measurement. Our results provide insight on the information that the in-phase part provides about the distribution of electrical conductivity with depth.

How to cite: Carrizo, M., Slob, E., and Werthmüller, D.: Exploiting the full information of the coupling ratio measurements in frequency domain electromagnetic induction instruments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17211, https://doi.org/10.5194/egusphere-egu23-17211, 2023.

08:50–09:00
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EGU23-1514
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On-site presentation
Octavio Castillo Reyes and Pilar Queralt

Electromagnetic imaging has been perfected to investigate the subsurface over the past three decades. Developing numerical schemes, algorithms, and easy access to supercomputers have supported innovation throughout the geo-electromagnetic community. Now, with the Exascale computing era dawning upon us, even more accurate, clearer, and faster data will be within our reach. However, numerical methods, computational strategies, and codes must be reshaped and honed to prepare for the upcoming challenges. Europe is making a huge effort in the strategic global race to Exascale, with large investments in the infrastructure. From the point of view of science and services, this unprecedented infrastructure opens a myriad of possibilities but, at the same time, the transition is challenging and requires a joint effort from (geo)scientists, mathematics, software engineers, and data analysts. Herein, we discuss the symbiotic relationship between numerical methods and computational strategies for EM imaging in the Exascale era. We focus on the need to explore all the alternatives of technologies, applications, and expertise transfer to propel the high-performance electromagnetic mapping landscape forward.

How to cite: Castillo Reyes, O. and Queralt, P.: High-performance electromagnetic mapping in the exascale era, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1514, https://doi.org/10.5194/egusphere-egu23-1514, 2023.

09:00–09:20
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EGU23-6874
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ECS
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solicited
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On-site presentation
Romain Corseri, Sverre Planke, Leiv Jacob Gelius, Jan Inge Faleide, and Kim Senger

Magnetotellurics (MT) image the Earth’s electrical resistivity down to the mantle but is rarely used for investigation of offshore rifted margins. In such setting, the stretched lithosphere is altered by distinct tectono-thermal processes such as partial melt, hydration, or chemical alteration. However, lower crustal and upper mantle often display similar seismic velocities, density, and magnetic properties. Integration of resistivity models from MT data can lift this ambiguity in a hyper-extended rift system. In this project, we use an extensive marine MT database consisting of 337 receivers located along seven regional transects, emanating from ~70 000 km2 of 3-D CSEM surveys acquired for hydrocarbon exploration in the SW Barents Sea. 3D inversion of long period, marine MT data (1 – 3000 s) is performed on 104 receivers located along two, ~300 km long transects located over the Bjørnøya Basin, located ~300 km offshore northern Norway. We also apply 1D Bayesian inversion to a selection of receivers as an alternative to the deterministic approach for a more comprehensive exploration of the solution space.

The resolving power of MT data is assessed with synthetic tests in an archetypal rift system where ample crustal thickness variation occurs. The results highlight that our MT data sense the transition from necking to hyper-extended domain where the crust (<~10 km) is not reconstructed by 3D inversion. In the Bjørnøya Basin – the northernmost member of a hyper-extended Cretaceous basin chain in the North Atlantic – seismic interpretation is used to assign a stratigraphic level to two prominent conductors in the resistivity models: (1) 0.1-1 Ω.m within Lower Cretaceous marine shales buried at 10-15 km depth (2) 1-10 Ω.m within the uppermost mantle. The bulk resistivity of a 2-phase, fluid-rock model emphasizes that seawater as a sole pore fluid phase is not conductive enough to explain the magnitude of the two conductors. A 25% serpentinization of mantle rocks can account for a fivefold rise in salinity of the residual fluid and is compatible with density and seismic velocities in the Bjørnøya Basin. Samples from fossil margins in the Alps and Pyrenes shows contamination of post-rift sediments pore fluids by mantle elements, highlighting the mobility of mantle-reacted fluids in hyper-extended systems. High-salinity fluid can ascend and mix with seawater in pore spaces of the sediments, supporting our proposed model of saline fluid circulation in hyper-extended basins.

How to cite: Corseri, R., Planke, S., Gelius, L. J., Faleide, J. I., and Senger, K.: Magnetotelluric image of a hyperextended and serpentinized rift system in the SW Barents Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6874, https://doi.org/10.5194/egusphere-egu23-6874, 2023.

09:20–09:30
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EGU23-8414
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On-site presentation
Ümit Avşar, Gökhan Karcıoğlu, Tülay Kaya Eken, and Turgay İşseven

Anatolia has been the center of civilizations throughout history, as well as a laboratory for geoscientists in terms of its geological history. The eastern Mediterranean region and Anatolia are located at the intersection of different tectonic plates controlled by the African-Eurasian convergence, which continues along the Cyprus and Aegean (Hellenic) arcs in the southwest and resulted in collision in the east. The interrelation between Cyprus and Aegean arcs remains a topic of discussion among scientists. It is thought that the intersection area of ​​the Aegean and Cyprus arcs, located beneath the Western Anatolia and Isparta Angle (IA), is a slab tear that causes asthenospheric upwelling in SW Anatolia and IA. The reflection of this tear on the surface occurs as a STEP fault type and is represented by the Fethiye - Burdur Fault Zone (FBFZ) forming the western border of IA and Akşehir Fault Zone (AFZ) forming the eastern border of the region. Isparta Angle, influenced by the aforementioned tectonic systems, is located between the FBFZ and AFZ as a reverse triangle shape. Therefore, besides the main border fault zones, there are various normal and reverse faults and related graben-horst structures in the region.    

IA is located at where opening and closing of various oceans took place. The main geological basement consists of autochthonous and allocton units. Autochthonous units are called as Beydağları and Anamas - Akseki carbonate platforms. Allocton units were transported and obducted over these carbonate platforms in different geological times and they can be ordered as Lycia nappes, Antalya nappes and Beyşehir-Hoyran-Hadim nappes, respectively. There are various basin formations observed throughout the region, related to nappe emplacements and Cyprus subduction zone back-arc tensional forces before Miocene, and extensional tectonism which became effective after Miocene.

The magnetotelluric (MT) method involves the measurement of the time variations of the orthogonal components of natural electric and magnetic fields, which contain information about the electrical resistivity structure from crustal to upper mantle depths. The superiority of the MT method in determining conductivity differences makes it possible to detect aqueous fluids and magma (partial melting). In active tectonic regions such as IA, where various tectonic systems intersect and an asthenospheric upwelling is proposed where aqueous fluids, partial melting or both could be the reason for high conductivity, magnetotellurics is well suited method to study fault-related structures and tectonic processes.

In this study, magnetotelluric data were collected in 4 profiles at 47 stations and inverted by using ModEM software to reveal 3D subsurface conductivity structure of the area. The most striking feature is a lower crust conductor located mostly in western part of the region and an upper crustal conductive structure which is related to the lower one imaged in the region. This upper-crust conductor structure reaches up to the surface beneath the main fault zones. The basement structures which consist of nappes, carbonate platforms are imaged as resistive zones and their depths are clearly imaged in the recovered resistivity models.

How to cite: Avşar, Ü., Karcıoğlu, G., Kaya Eken, T., and İşseven, T.: The imaging of the tectonic structure of Isparta Angle by 3D inversion of Magnetotelluric Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8414, https://doi.org/10.5194/egusphere-egu23-8414, 2023.

09:30–09:40
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EGU23-11254
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Virtual presentation
Younes Ghasemipour, Sayyed Mohammad Abtahi Forooshani, and Hamzeh Sadeghisorkhani

The Sabalan geothermal in northwestern Iran is the most well-known geothermal in the country. Due to the Sabalan caldera's structures and dozens of younger faults, the area consists of highly fractured rocks. Besides, processing the aeromagnetic data in the area revealed some other hidden faults. To investigate the effect of the faults on the geothermal system, we conducted a dimensionality analysis based on magnetotelluric impedance and phase tensors from two magnetotelluric datasets. The datasets were surveyed at different times, one in the dry season of June 1998 and the other in the wet season of November 2007. The dimensionality behavior obtained from the datasets differs significantly. We realized that the discrepancy was due to the time of conducting the magnetotelluric survey. For instance, the polar diagrams computed from the dry season data showed a better correlation with fault strikes in some of the frequencies where the wet season data polar diagrams were less sensitive to the fault orientations. Besides, the strike of a hidden fault extracted from aeromagnetic data was apt to the extension of Zxy's polar diagram. Furthermore, the dimensionality analysis and skew angle in dry season data demonstrate a 2D to 3D media, whereas the wet season data showed a 1D to 2D earth. We deduced that faults have a more significant role in providing resistivity contrast in dry seasons and hence, a better illustration for the geoelectric strike.

How to cite: Ghasemipour, Y., Abtahi Forooshani, S. M., and Sadeghisorkhani, H.: Investigation of the influence of faults on geoelectric strikes and dimensionality analysis of MT data in the Sabalan geothermal area, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11254, https://doi.org/10.5194/egusphere-egu23-11254, 2023.

09:40–09:50
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EGU23-12872
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ECS
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Virtual presentation
Mohammad Hajheidari, Sayyed Mohammad Abtahi Forooshani, Nader Fathianpour, Keytash Moshtaghian, and Hojatollah Tavakoli Harandi

The Varton geothermal is located circa 70 kilometers northeast of Isfahan, central Iran. The study area consists of highly fractured rocks with argillic alteration zones and some hot springs. Here, we conduct a magnetic and magnetotelluric data survey to study the effect of the fractures on the hydrothermal convection system. The magnetic data processing exposed two parallel main faults with NW-SE strike in the northern and southern borders of the area. Here, we used nine magnetotelluric (MT) stations along a profile perpendicular to the main faults. Dimensionality analysis of MT impedance and phase tensors in the stations indicated a media with two-dimensional structures. However, 1D MT data inversion revealed a three-layered earth beneath most stations, though the layers' thickness and resistivities varied along the profile. Also, 2D MT data inversion results showed that the resistivity between the two main faults was significantly smaller than zones beyond the faults. However, a large zone with low resistivity was close to the southern fault. Besides,  a shallow layer overlain a thin conductive layer with a resistivity of one ohmm or less. In depths more than 500 m, the resistivity noticeably increased gradually to 1000 ohmm. According to the mentioned results, we deduce that the southern fault is the main feeding fault for the geothermal system. Furthermore, the layer with the lowest resistivity correlates with clay alteration and could be the clay cap of the reservoir. Therefore, the deeper resistive rock is the geothermal reservoir.

How to cite: Hajheidari, M., Abtahi Forooshani, S. M., Fathianpour, N., Moshtaghian, K., and Tavakoli Harandi, H.: MT data inversion and dimensionality analysis in Varton geothermal central Iran, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12872, https://doi.org/10.5194/egusphere-egu23-12872, 2023.

Posters on site: Wed, 26 Apr, 16:15–18:00 | Hall X2

Chairpersons: Duygu Kiyan, Shunguo Wang
X2.267
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EGU23-4212
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ECS
Shan Xu, Chaojian Chen, Alexey Kuvshinov, Mikhail Kruglyakov, Rafael Rigaud, and Xiangyun Hu
Vertical magnetic transfer functions (tippers) observed at a global/continental net of geomagnetic observatories can be used to image the electrical conductivity structure of the Earth down to a depth of around 200 km. We estimated tippers at 54 geomagnetic observatories across China, aiming eventually to invert them in terms of subsurface three-dimensional (3-D) conductivity distribution. Strikingly, we obtained enormously large tippers at three inland observatories in southwest China. Large tippers are often observed at coastal observatories due to the high lateral conductivity contrast between resistive continental bedrock and conductive seawater. However, tippers at those mentioned above observatories appeared to be a few times larger than coastal tippers. Moreover, as far as we know, such large tippers (reaching value 3) were never reported in any region of the world. We perform 3-D electromagnetic simulations mimicking the geological setting of the region and demonstrate that the enormously large tippers are feasible and can be attributed to a current channelling.

 

How to cite: Xu, S., Chen, C., Kuvshinov, A., Kruglyakov, M., Rigaud, R., and Hu, X.: Enormously large tippers observed in South-West of China. Can realistic 3-D modeling reproduce them?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4212, https://doi.org/10.5194/egusphere-egu23-4212, 2023.

X2.268
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EGU23-4381
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ECS
deep learning based sferics recognition for AMT dataprocessing in the dead band
(withdrawn)
enhua jiang, rujun chen, xinmin wu, jianxin liu, debin zhu, and weiqiang liu
X2.269
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EGU23-5006
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ECS
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Paula Rulff, Thomas Kalscheuer, and Dominik Zbinden

We present a synthetic inversion study illustrating two approaches which help to deal with heterogeneous sensitivities in 3D frequency-domain controlled-source electromagnetic inverse problems.

Using edge-based vector finite-element approximations on tetrahedral meshes and a preconditioned non-linear conjugate gradient algorithm, we invert for impedance tensor elements generated by a set of two coincident perpendicularly oriented horizontal electric or horizontal magnetic dipole sources. Depending on the number and locations of sources and the choice of impedance tensor components used for inversion, the sensitivity patterns can differ significantly. Measurement setups with a small number of sources, but many receiver stations at the surface covering near-field, transition zone and far-field, are often deployed for land-based controlled-source electromagnetic measurements. Such a setup can result in accumulated sensitivities close to the sources and receivers, which implies strongest model updates in these regions and can mislead the inverse algorithm to a search direction, where no physically meaningful model can be produced nor the data are fitted.
 
In order to mitigate the influence of strong sensitivities near sources and receivers on the inversion process, we apply an efficient preconditioner and customisable weights in the model regularisation matrix. The preconditioner is updated with the Broyden-Fletcher-Goldfarb-Shanno algorithm using the diagonal of the approximate Hessian matrix as start preconditioner. The latter is computationally expensive to obtain, but aims at finding a favourable search direction for the inverse algorithm already in early iterations and distributing the model update more evenly in the domain. To account for the sensitivity loss with depth, we implemented a depth weighting functional in the model regularisation term. The approach is based on counteracting the exponential and geometrical decay of the electromagnetic fields with depth and distance from the sources. In practical, we increase the smoothing in the shallow part of the model close to the source locations, where no structure is expected. We present synthetic examples indicating that this approach is an efficient way of helping the inversion to converge, obtaining a reliable model and resolving structure at depth.

How to cite: Rulff, P., Kalscheuer, T., and Zbinden, D.: Counteracting sensitivity accumulation near source and receiver locations in 3D inversion of controlled-source electromagnetic data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5006, https://doi.org/10.5194/egusphere-egu23-5006, 2023.

X2.270
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EGU23-5856
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ECS
Uula Autio, Jochen Kamm, Tero Niiranen, and Ilkka Lahti

New broadband magnetotelluric (MT) data were acquired within the BATCircle2.0 project (WP1) in the Kuusamo Schist Belt (KuSB), northeastern Finland. The MT measurements aim to outline the regional geological structures of the belt together with potential field and petrophysical data. The new knowledge on the large-scale structures of the KuSB helps to understand its evolution and holds clues to mineralization processes of the area. A 20 km wide and 70 km long window crossing the KuSB in the NW–SE direction was selected as the survey area from which new MT and gravity data were collected. Here, we present the first results from the MT part of the study.

The survey area is located in the KuSB that is a southern extension of the Central Lapland Greenstone Belt (CLGB). The CLGB is one of the largest Proterozoic greenstone belts in the world. It consists of a Palaeoproterozoic (2.5–1.97 Ga) volcanic and sedimentary cover that was deposited on the Archaean (> 2.5 Ga) basement. Rifting, magmatism, deposition of sedimentary sequences occurred 2.44–2.0 Ga. Deformation and metamorphism were related to Svecofennian orogenic events 1.92–1.79 Ga. The KuSB area is particularly prospective for Co-Cu-Au-U-REE deposits and several such mineralizations are known in the area.

The collected MT dataset consists of ca. 150 sites with site spacing of 1–5 km. A profile with denser site spacing (1 km) was supported by sparse (5 km) off-profile sites. From time series processing high quality transfer functions were obtained in the period range 0.003–256 s. Phase tensor analysis shows that the regional electrical dimensionality is mainly 3D. First 3D inversions of the MT data set using the ModEM code (Kelbert et al., 2014) indicate the existence of a crustal conductor at several kilometers depth in the northern part of the study area. 

References:

Kelbert, A., Meqbel, N., Egbert, G., Tandon., K., 2014. ModEM: A modular system for inversion of electromagnetic geophysical data. Computers & Geosciences, Volume 66, May 2014, Pages 40-53

 

How to cite: Autio, U., Kamm, J., Niiranen, T., and Lahti, I.: Magnetotelluric survey in the Kuusamo Schist Belt, Northeastern Finland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5856, https://doi.org/10.5194/egusphere-egu23-5856, 2023.

X2.271
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EGU23-5892
Chaojian Chen, Alexey Kuvshinov, Mikhail Kruglyakov, Federico Munch, and Rafael Rigaud

In this study, we present a quasi-1D tool to simultaneously invert multi-source magnetic transfer functions (TFs), including tippers, solar global-to-local transfer functions (TFs) originating from the signals due to ionospheric source, and global Q-responses originating from the signals due to magnetospheric source. We jointly invert the aforementioned TFs to constrain the local 1-D conductivity structures beneath three islands in the Atlantic (Tristan da Cunha), Indian (Cocos), and Pacific (Oahu) Oceans. The recovered conductivity profiles appeared to be consistent with the presence of upper mantle plumes beneath the Tristan da Cunha and Oahu Islands. Our results indicate resistive lithosphere of different thicknesses beneath considered three islands, in agreement with the age of the ocean floor. Besides, new conductivity profiles suggest warmer-than-average mantle temperatures and the presence of a small fraction of melt beneath Tristan da Cunha Island. At the same time, the conductivities beneath Cocos Island are in good agreement with estimates expected for ambient mantle conditions.

How to cite: Chen, C., Kuvshinov, A., Kruglyakov, M., Munch, F., and Rigaud, R.: Constraining the crustal and mantle conductivity structures beneath islands by a joint inversion of multi-source magnetic transfer functions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5892, https://doi.org/10.5194/egusphere-egu23-5892, 2023.

X2.272
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EGU23-7407
Katrin Schwalenberg, Hendrik Mueller, and Udo Barckhausen

Deep-sea hydrothermal vent fields associated with the formation of seafloor massive sulfides (SMS) may become a future source of high-tech minerals such as Cu, Ni, Pb, Co, and REE, which are all in demand for the energy transition away from hydrocarbon resources. The identification and evaluation of the deposits in the deep ocean is a needle in a haystack problem. They are relatively small (size of a soccer field) and form in complex terrain at mid-ocean ridges, island arcs and back-arc spreading centres. Active hydrothermal vents are often accompanied with black smokers and have an abundant, environmental sensitive fauna and low mineral potential. Inactive and extinct vent sites are generally missing characteristic seafloor expressions and distinct vent fauna, and may be hidden under a thin layer of sediments. Thus, video observations and sampling may not be sufficient to evaluate the size and spatial extent of the SMS deposit. Massive sulfides are known to belong to the group of natural rocks with the highest electrical conductivity due to their electronic surface conduction, which makes them an interesting target for electromagnetic and electrical methods. BGR’s GOLDEN EYE electromagnetic deep-sea profiler has been developed to collect a variety of marine frequency domain CSEM loop data and electric dipole-dipole data in the German license areas for SMS exploration located in the Indian Ocean. The data are analyzed in terms of frequency, thus depth-depending conductivity models, chargeability and self-potential effects. The latter has been also measured with two deep-towed Vulcan E-field receivers. Both systems reveal significant anomalies over visually identified sulfide targets, but also in so far uncovered areas. We present details on instrumentation, data analysis, and preliminary results from resent cruises.

How to cite: Schwalenberg, K., Mueller, H., and Barckhausen, U.: Electromagnetic signatures of deep-sea massive sulfide deposits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7407, https://doi.org/10.5194/egusphere-egu23-7407, 2023.

X2.273
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EGU23-9485
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ECS
Rafael Rigaud, Matthew Joseph Comeau, Michael Becken, Alexey V. Kuvshinov, Shoovdor Tserendug, Erdenechimeg Batmagnai, and Sodnomsambuu Demberel

Intracontinental deformation and intraplate volcanism, which occur far from tectonic plate boundaries, are not fully understood. Their origin and evolution are linked by crust-mantle interactions and mantle convection dynamics. Mongolia is an ideal natural laboratory for studying such processes because it is located far into the continental interior, several thousand kilometres from major tectonic margins.

 

To the north is the Siberian craton, which is relatively stable, to the northeast is an extensional regime near the Baikal rift zone, which stretches for more than one thousand kilometres, and to the south are the North China and Tarim cratons, which have northward-directed motion creating a compressional regime. Central Mongolia, which contains a high plateau (with indications of vertical motion), is characterized by a shallow lithosphere-asthenosphere boundary that deepens at the edges, notably northwards towards the Siberian Craton. Continental intraplate basaltic volcanism of Cenozoic age exists across central and northern Mongolia, with several large concentrations within the Hangai region.

 

As part of an ongoing project, we are investigating the lithospheric properties and lithospheric architecture beneath this region with magnetotelluric measurements and three-dimensional models of electrical resistivity. In addition, thermo-mechanical numerical modelling, with geophysically-guided constraints, is being used to provide valuable insight by testing different hypotheses for the temporal evolution and dynamic processes -- such as whether an upwelling asthenosphere and/or lithospheric removal could realistically be a consequence of delamination, edge-driven convection mechanisms from a lithospheric step, or some combination.

 

Towards these goals, geophysical models that image the transition from thin lithosphere to thick lithosphere (and its geometry), believed to occur beneath northern Mongolia, are beneficial. There exists a wealth of recent geophysical data across central Mongolia, in addition to petrological data. This includes a temporary broadband seismic array that covers the Gobi, Hangai, and Hovsgol regions.

 

In this presentation, we will report on 79 new magnetotelluric measurements acquired in 2022 in northern Mongolia across the Hovsgol and Darhad regions, as well as 77 new measurements acquired from 2020-2022 in central-east Mongolia (Bulgan, Arvaikheer). The acquired data are very good quality with low noise, a clear benefit of the remote location. Recordings were carried out at each location for approximately 1-5 days. The data typically had reliable periods up to 1,000 - 8,000 s. The new data will, ultimately, be integrated into the previously collected dataset across central Mongolia (Hangai, Bayankhongor, and Gobi-Altai), which consists of 328 measurement locations (thus approximately 500 total), which covers a total area of, currently, approximately 1000 km by 800 km. This is a notably large area, within the realm of several large regional and national magnetotelluric (and seismic) surveys. Furthermore, the data across northern Mongolia fill the last gap in a remarkable transect of existing magnetotelluric data that extends approximately 4,000 km from across the Siberian Craton to across the Tibetan Plateau.

How to cite: Rigaud, R., Joseph Comeau, M., Becken, M., V. Kuvshinov, A., Tserendug, S., Batmagnai, E., and Demberel, S.: Magnetotelluric Data Across Mongolia: Implications for Intracontinental Deformation and Intraplate Volcanism — Report on New Measurements, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9485, https://doi.org/10.5194/egusphere-egu23-9485, 2023.

X2.274
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EGU23-11165
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ECS
Shunguo Wang, Steven Constable, Valeria Reyes-ortega, and David T. Sandwell2

Seafloor fracture zones are the inactive extensions of transform faults that represent a discontinuity in seafloor age, temperature, and bathymetry. Their structures and tectonic features provide important information about lithospheric evolution. The age contrast across the fracture zone produces differential subsidence resulting in lithospheric flexure with uplift on the young side and subsidence on the old side. There is still debate on whether a fracture zone is significantly weaker than the surrounding lithosphere.  Some models predict small-scale convection beneath the FZ due to the sharp thermal contrast. A magnetotelluric (MT) survey over the Mendocino fracture zones (MFZ) was carried out 600 km away from the US west coast in 2018. The primary objective is to determine whether changes in the electrical resistivity across the MFZ are caused by temperature variations or other factors at the LAB. There is a strong crust age contrast at different sides of the MFZ. The northern side, younger with a crust age of 6.5 Ma, is formed at the Gorda Ridge with depths of about 3 km. The southern side, older with a crust age of 33 Ma, is part of the Pacific plate with depths of about 4 km. On both sides of MFZ, seamounts are observed in the study region, which indicates off-axis magma upwelling. Two-dimensional (2D) inversion of MT data was done to construct a 2D resistivity model across MFZ. The inversion can fit the data to an RMS of 1.8 with an error floor of 5 % on the MT impedance tensor. The model shows strong resistivity contrasts at the depths of 30-80 km on both sides of MFZ. The resistivity contrast at such depths is likely attributed to partial melt and temperature since composition is most likely similar at both sides of MFZ. Other conductive anomalies are also observed at shallow depths along the profile, which collocates with seamounts at the study region, especially near the southern end of our MT profile. Therefore, the conductive anomalies at the shallow depths likely present partial melts driven by upwelling magma.

How to cite: Wang, S., Constable, S., Reyes-ortega, V., and Sandwell2, D. T.: Resistivity imaging of Mendocino Fracture Zone using marine magnetotelluric data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11165, https://doi.org/10.5194/egusphere-egu23-11165, 2023.

X2.275
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EGU23-12197
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ECS
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Hossam Marzouk, Tarek Arafa-Hamed, Michael Becken, Mathew Comeau, and Abdallah Ibrahim

Northeast Africa, which today includes the Arabian-Nubian Shield and the Saharan Metacraton, experienced a complex and long history of tectonic events. These include cratonization, which resulted in thickening of the lithosphere and formation of stable cratons, and decratonization, which occurred as a result of the remobilization and reactivation of the tectonic domains through subsequent orogenies, or destruction of the cratonic root during extensional events. One outstanding question is the present-day architecture of the lithosphere across this region, including the location of important tectonic boundaries. Several geophysical investigations have been conducted to study the lithosphere, including density and velocity modeling; however, they have mainly focused on the hydrocarbon-rich areas offshore and onshore close to the western coast of the Gulf of Suez, in addition to some small regional-scale studies.

We present a tectonic model of the Arabian-Nubian Shield and Saharan Metacraton derived, in part, from a 3D electrical resistivity model generated from magnetotelluric measurements acquired along a 700 km long profile across the central part of Egypt. The profile, roughly west-east, consists of 57 measurements, a subset of a larger dataset acquired in the region. The profile crosses the main tectonic boundaries in Egypt: the Arabian Nubian Shield (ANS) in the eastern part, the Nile River in the central part, and the Saharan Metacraton (SMC), in addition to its cratonic remnants (Al-Kufra), in the western part. The profile runs approximately along a line from Dahkla to Kharga, across to Qena, and towards Hurghada on the coast. On average, the measurement spacing is approximately 10 km, although it is denser in some regions (e.g., near ANS) and sparser in others (e.g., near Qena) due to local conditions.

The data were acquired in campaigns carried out in autumn 2019, spring 2020, spring 2021, and spring 2022. The measurements used Metronix data loggers (ADU07e) and Metronix induction coils along with locally developed copper-copper sulphate electrodes to measure the electric field. Most sites were recorded for 2-5 days. The sampling rate used was 512 Hz. Periods up to 1,000 – 5,000 s were recorded. The data are generally considered to be of good quality and had low noise; this is primarily due to the lack of urban electrical noise in most of the survey area.

Dimensionality analyses suggest a 3D character for long-period data, particularly in the ANS area, that requires the use of full 3D inversion to properly describe all aspects of the data. Several sensitivity tests were carried out to validate the robustness of the features in the 3D electrical resistivity model. A comparison of the resistivity model with other geophysical models in this region (including density and velocity models) shows a good correlation for the location of the cratonic boundary, which has a clear resistive electrical signature.         

How to cite: Marzouk, H., Arafa-Hamed, T., Becken, M., Comeau, M., and Ibrahim, A.: Tectonic model of the Arabian-Nubian Shield and the Saharan Metacraton, Northeast Africa, derived from magnetotelluric data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12197, https://doi.org/10.5194/egusphere-egu23-12197, 2023.

X2.276
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EGU23-16297
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ECS
Duygu Kiyan, Colin Hogg, Joan Campanya, Christopher J. Bean, Javier Fullea, Sean P. Blake, John Malone-Leigh, Peter T. Gallagher, Volker Rath, Alan G. Jones, and Ray Scanlon

Quantifying and de-risking the exploration for geo-resources require knowledge of the subsurface. This is true for example for both mineral and geothermal exploration. Often that knowledge is built up by local geophysical studies on areas of interest but the broad deeper context and controls for the system are often missing due to a lack of appropriate deep (e.g., >2 km) geophysical imagery. The primary goal of this project is to develop a deep (range 5-100 km) 3-D electrical conductivity model of Ireland’s crust and uppermost mantle using magnetotelluric (MT) method. Deep probing MT imaging yields information on the structure, composition and temperature of Earth’s crust and upper mantle, and can detect processes associated with mineralisation and areas of high temperature and or permeability related to promising geothermal targets. It will also help better illuminate the deep geology of Ireland, particularly in the context of the mechanisms of the Caledonian and Variscan Orogenies that formed Ireland, the emplacement of its sizable granites, and the intraplate basaltic volcanism that followed the opening of the North Atlantic and created the famous Giant’s Causeway and other features. MT experiments have been conducted in Ireland since 1980s. These include the Irish Magnetotelluric Profile in the late 1980s, and the Irish Magnetotelluric Lithospheric Experiment ISLE-MT in the mid-2000s. In the framework of Space Weather ElectroMagnetic Database for Ireland, long-period MT (LMT) data were acquired at over twenty stations in 2018. Since June 2019, new LMT data have been acquired at twelve stations. The recent project HIbernian Regional GeoElectrical Structure Hi-RES aims to complete an all-island dataset of LMT soundings by acquiring an additional 22 sites across Ireland, expanding on previous MT campaigns. This contribution will present analysis and 3-D modelling results of these datasets. 

How to cite: Kiyan, D., Hogg, C., Campanya, J., Bean, C. J., Fullea, J., Blake, S. P., Malone-Leigh, J., Gallagher, P. T., Rath, V., Jones, A. G., and Scanlon, R.: 3-D Magnetotelluric Assessment of the Geo-resources Potential of the Irish Crust, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16297, https://doi.org/10.5194/egusphere-egu23-16297, 2023.

X2.277
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EGU23-17509
Time-Lapse Marine CSEM Modeling in the Framework of Linear and Non-Linear Approximations
(withdrawn)
Maryam Bayat, Reza Ghanati, and Ivan Lokmer
X2.278
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EGU23-10339
Tao Ye, Kiyan Duygu, Brian O’Reilly, Patrick Meere, Colin Hogg, Javier Fullea, Christopher Bean, Sergei Lebedev, Emma Chambers, Meysam Rezaeifar, Gaurav Tomar, and Aisling Scully and the DIG team

The DIG (De-risking Ireland’s Geothermal Energy Potential) project aims to better understand Ireland’s low-enthalpy geothermal energy potential by integrating inter-disciplinary and multi-scale datasets (Kiyan et al., 2022; Chambers et al., 2022). One aim of the project is to evaluate the geothermal energy potential of the Upper Devonian Munster Basin within the Variscides of southern Ireland. A more specific objective is to focus on the Mallow warm springs area (MWSA) which is sited along the Killarney-Mallow Fault Zone (KMFZ).

Two parallel magnetotelluric (MT) profiles have been deployed across the east-northeast trending KMFZ in the MWSA since November 2021 to directly image fault conduits and fluid aquifer sources at depth, within a convective/conductive region associated with the known occurrence of warm thermal springs. This will determine the scale of the geothermal anomaly and hence will evaluate the potential for local- and industrial-scale space heating in the local-scale survey locality.

To eliminate the electromagnetic noise from the acquired MT time-series data, we have made efforts to improve the data quality by not only using the new generation Phoenix Geophysics MTU-5C systems but also processing these time-series data with two different processing software; (i.e., FFProc, an improved multivariate robust statistical data processing software (Castro et al., 2021) and EMPower, a commercial remote-reference software from Phoenix Geophysics).

The 2-D inversion of these data reveals a striking vertical fault conductor zone (FCZ) extending to depths of at least 4 km beneath the KMFZ. The corresponding 3-D inversion model for these data along the two profiles further confirms the existence of the FCZ. Based on our preliminary results, we propose that the KMFZ is probably the main fault conduit associated with the Mallow warm springs area and the FCZ delineates the fluid pathways associated with the fault zone.

How to cite: Ye, T., Duygu, K., O’Reilly, B., Meere, P., Hogg, C., Fullea, J., Bean, C., Lebedev, S., Chambers, E., Rezaeifar, M., Tomar, G., and Scully, A. and the DIG team: Magnetotelluric investigation of the geothermal resources of South-West Ireland: DIG Project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10339, https://doi.org/10.5194/egusphere-egu23-10339, 2023.