The 2D resistivity modelling on north sumatran fault structure by using magnetotelluric data

<p>Regional magnetotelluric (MT) survey had been conducted to image resistivity structures beneath Toba Caldera, Indonesia. A crustal-scale 2D inversion model is generated from ten MT stations with extended recording time, deployed along NE-SW regional line to cross perpendicularly both the Caldera and the nearby regional strike-slip fault system, the Sumatran Fault. High resistivity background is likely related to Palaeozoic rocks which is basement of the Tertiary sediments and the Quaternary volcanics. The most noticeable conductive anomaly is located between 10-20 km deep, interpreted as the main magma reservoir beneath the region. An intermediate, less than 10 km-deep, less conductive anomaly beneath the Caldera is interpreted as shallow magma chamber affected by the last major eruption. Shallow, less than 2 km-deep conductive layers are associated either with hydrothermal clay cap beneath the Caldera, or sedimentary formations of the nearby basins. Other conductive anomaly is spatially associated with the Sumatran Fault which located 15 km away from the Caldera. Parameter plots of some stations are consistent with the orientation of basement structures, while the others may be affected by more complex caldera structures. A conceptual model of magma plumbing system beneath the Caldera is then interpreted from the combination of regional resistivity structures, surface geology, and available seismic tomography.</p>

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Geophysical characterization of the Menengai volcano, Central Kenya Rift from the analysis of magnetotelluric and gravity data

Geophysics ◽

10.1190/geo2011-0419.1 ◽

2013 ◽

Vol 78 (4) ◽

pp. B187-B199 ◽

Cited By ~ 2

Author(s):

Antony Munika Wamalwa ◽

Kevin L. Mickus ◽

Laura F. Serpa

Keyword(s):

Gravity Data ◽

Gravity Models ◽

High Resistivity ◽

Geothermal System ◽

Low Density ◽

Fracture Density ◽

Density Region ◽

Magnetotelluric Data ◽

Low Resistivity ◽

2D Resistivity

In this study, we qualitatively analyze detailed gravity and broadband magnetotelluric data in and surrounding the Menengai volcano of the East African rift in Kenya to assess geothermal potential of the region. Three-dimensional gravity models obtained by inverting residual gravity anomalies and 2D resistivity models obtained by inverting the transverse electric and transverse magnetic magnetotelluric modes show several common features. Our models show that a low-resistivity zone above a higher resistivity zone correlates with a low-density region located 1–4 km beneath the volcano. These zones may be related to a high temperature gradient or hydrothermally altered, fractured rocks. Additionally, a low-resistivity ([Formula: see text]) and a low-density region located approximately 4–6 km below the volcano may be related to molten material that is the source of heat for the geothermal system. The low-resistivity ([Formula: see text]) regions that correlated with a denser ([Formula: see text]) region within the caldera are bounded by high-resistivity ([Formula: see text]), high-density ([Formula: see text]) volcanic units implying that the dense and electrically resistive volcanic material is relatively cool and lacks significant fluid content that can lower resistivity. At shallow depths, 0.5–1.5 km below the caldera, a low-resistivity and low-to-moderate density region is interpreted as a zone with high fracture density that consists of clay minerals resulting from hydrothermal alteration. These results agree well with the results from previous seismic studies on the depth of the suggested molten rocks.

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2D Modeling of Seulawah Agam Geothermal Field Based on Magnetotelluric (MT) Data

Journal of Aceh Physics Society ◽

10.24815/jacps.v8i2.12871 ◽

2019 ◽

Vol 8 (2) ◽

pp. 61-65

Author(s):

Irfan Putra ◽

Nazli Ismail ◽

Marwan Marwan

Keyword(s):

Geothermal Field ◽

Magnetotelluric Data ◽

2D Modeling ◽

Te Mode ◽

Tm Mode ◽

Top Soil ◽

Resistivity Variation ◽

2D Data ◽

Mode Tm ◽

2D Resistivity

Telah dilakukan pemodelan 2D data Magnetotellurik (MT) di Gunung Api Seulawah Agam. Penelitian ini bertujuan untuk mendapatkan model konseptual lapangan panas bumi Gunung Api Seulawah Agam berdasarkan model resistivitas 2D. Data fungsi transfer MT yang digunakan yaitu dari rentang frekuensi 2,34 - 320 Hz yang terdiri dari 7 titik stasiun pengukuran. Data titik pengukuran terdiri dari nilai intensitas medan listrik dan intensitas medan magnet yang memiliki 28 frekuensi. Total panjang lintasan pengukuran yaitu sepanjang 27,7 km. Lintasan pengukuran memotong Gunung Api Seulawah Agam dari arah Selatan ke Utara. Data hasil pengukuran yaitu berupa nilai resistivitas semu dan fase yang kemudian dimodelkan menggunakan kode REBOCC. Terdapat 3 model yang dihasilkan dari proses inversi data MT menggunakan REBOCC yaitu mode TE, mode TM dan mode TE+TM. Model mode TE+TM merupakan model yang paling bagus karena menghasilkan model yang lebih jelas dan smooth bila dibandingkan dengan model pada mode TE dan mode TM. Hasil model konseptual menunjukkan bahwa pada lapisan pertama yaitu lapisan top soil (lapisan teratas) memiliki nilai resistivitas sebesar 20 - 60 Ω.m, yang terdapat pada jarak 6 - 23 km. Lapisan kedua yaitu lapisan clay/caprock dengan nilai resistivitas relatif rendah yaitu lebih kecil dari 10 Ω.m, yang berada pada jarak 6 - 27,7 km. Lapisan clay/caprock memiliki sifat impermeabel dan konduktif. Selanjutnya lapisan ketiga yaitu lapisan reservoir dengan nilai resistivitas berkisar antara 10 - 100 Ω.m. 2D modeling of magnetotelluric data has been conducted at Seulawah Agam volcano. This study aims to obtain a conceptual model of Seulawah Agam geothermal field based on 2D resistivity model. The magnetotelluric data were measured in range of frequency from 2.34 to 320 Hz at 7 stations along a profile crossing the Seulawah Agam volcano. The length of the profile is 27.7 km with a direction from north to south. The apparent resistivity and phase of magnetotelluric transfers function were used for the 2D inversion modelling of REBOCC code. The inversion was carried out using TE-mode, TM-mode and TE+TM-mode to obtain a better model. The model inverted of TE+TM-mode has resolved well, resistivity variation of subsurface of the Seulawah Agam volcano area. The inverted model shows the top later has resistivity values from 20-60 Ω.m, which is interpreted as a top soil. The second layer is a layer of clay/caprock with a relatively low resistivity values of less than 10 Ω.m. The third layer is predicted as reservoir with resistivity values ranging between 10-100 Ω.m. Keywords: magnetotelluric method, resistivity, 2D model, REBOCC code and Volcano Seulawah Agam.

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Stochastic inversion of magnetotelluric data using a sharp boundary parameterization and application to a geothermal site

Geophysics ◽

10.1190/geo2011-0430.1 ◽

2012 ◽

Vol 77 (4) ◽

pp. E265-E279 ◽

Cited By ~ 30

Author(s):

Jinsong Chen ◽

G. Michael Hoversten ◽

Kerry Key ◽

Gregg Nordquist ◽

William Cumming

Keyword(s):

Bayesian Model ◽

Vertical Direction ◽

Adaptive Finite Element ◽

Sharp Boundary ◽

Lateral Direction ◽

Magnetotelluric Data ◽

Posterior Probability Distribution ◽

2D Resistivity ◽

Element Algorithm ◽

Quantifying Uncertainty

We developed a Bayesian model to invert magnetotelluric (MT) data using a 2D sharp boundary parameterization. We divided the 2D cross section into layers and considered the locations of interfaces and resistivity of the regions formed by the interfaces as random variables. We assumed that those variables are independent in the vertical direction and dependent along the lateral direction, whose spatial dependence is described by either pairwise difference or multivariate Gaussian priors. We used a parallel, adaptive finite-element algorithm to rapidly forward simulate frequency-domain MT responses of the 2D resistivity structure and used Markov chain Monte Carlo methods to draw many samples from the joint posterior probability distribution. We applied the Bayesian model to a synthetic case that mimics a geothermal exploration scenario. Our results demonstrated that the developed method is effective in estimating the resistivity and depths to interfaces and in quantifying uncertainty on the estimates. We also applied the developed method to the field MT data collected from the Darajat geothermal site in Indonesia. We compared our inversion results with those obtained from a deterministic inversion of 3D MT data; they are consistent even if the two inversion methods are very different and the amount of information used for inversion is different.

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Geothermal Reservoir Identification in Way Ratai Area Based on Gravity Data Analysis

Journal of Physics Conference Series ◽

10.1088/1742-6596/2110/1/012004 ◽

2021 ◽

Vol 2110 (1) ◽

pp. 012004

Author(s):

M Sarkowi ◽

R C Wibowo ◽

Karyanto

Keyword(s):

Density Distribution ◽

Gravity Data ◽

Bouguer Anomaly ◽

Geothermal Reservoir ◽

Gravity Gradient ◽

Low Density ◽

3D Inversion ◽

Magnetotelluric Data ◽

Fault Structure ◽

Geothermal Reservoirs

Abstract Gravity research in the Way Ratai geothermal prospect area was conducted to determine geothermal reservoirs, heat sources, and the structure of the geothermal reservoir. The research carried out includes 3D inversion modeling of gravity data. The Bouguer anomaly in the study area has 50 mGal to 120 mGal with low anomalies located in the southeast (Ketang and Kelagian), Northeast (Gedong Air, Sungai Langka, Gunung Betung) areas, and in the Pesawaran mountain area. The high anomaly is in Merawan – Hanuberak – Padang Cermin, Sumbersari and Kaliawi. The horizontal gravity gradient map analysis shows a pattern of fault structure trending northwest-southeast and southwest-northeast, according to the main fault structure in the area. 3D inversion modeling obtains a density distribution between 1.8 g/cc to 3g/cc with a low-density distribution in the south, Mount Pesawaran/Ratai, Gunung Betung, and Sidoharum. The location of the manifestation is 9 km southeast of the Mount Ratai/Pesawaran summit. The existence of geothermal reservoirs is estimated to be in the Lubuk Badak and Miwung Hills areas which are located between the peaks of Mount Ratai/Pesawaran and geothermal manifestations. This is supported by the low-density distribution in the area and the resistivity map from audio-magnetotelluric data.

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