Electromagnetic induction in geothermal fields and volcanic belts

García, Mario Martínez

doi:10.1007/bf01903485

Cited by 13 publications

(4 citation statements)

References 44 publications

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“…MT studies have proven particularly informative in tectonically active regions where fluids and/or melt are present within the lithosphere [e.g., Martinez‐Garcia , 1992; Jones and Dumas , 1993; Jiracek et al , 1995; Wannamaker et al , 1997a, 1997b; Jones , 1998; Partzsch et al , 2000; Ledo and Jones , 2001] because the presence of an interconnected melt or brine increases the bulk conductivity (decreases the resistivity) of the host rock by several orders of magnitude. For example, the laboratory measured resistivity value of dry granite at 500°C is ∼100,000 Ω m, but drops by 5 orders of magnitude when a saline fluid is added [ Olhoeft , 1981; Shankland and Ander , 1983].…”

Section: Magnetotelluric Methods and Prior Tibetan Mt Experimentsmentioning

confidence: 99%

Structure of the crust in the vicinity of the Banggong‐Nujiang suture in central Tibet from INDEPTH magnetotelluric data

et al. 2005

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[1] Magnetotelluric data from a 150-km-long profile crossing the Banggong-Nujiang suture (BNS), central Tibet, acquired as part of the International Deep Profiling of Tibet and the Himalaya (INDEPTH) project, have been examined for crustal and upper mantle structure. Strike and dimensionality analyses demonstrate that regional-scale electrical structures are two-dimensional and oriented approximately parallel to surface geological strike. As seen elsewhere in Tibet, the double thickness crust is generally characterized by resistive upper crust (hundreds to thousands of ohm meters) overlying conductive middle and lower crust (tens to hundreds of ohm meters), but in detail, there are lateral variations at all levels. Regionally, a northward transition from thick ($45 km) to thin ($15 km) resistive upper crust coincides with (1) the surface trace of the BNS, (2) a prominent strand of the Karakorum-Jiali fault system, (3) northward decrease in upper mantle seismic velocities and increase in attenuation, and (4) pronounced northward onset of seismic polarization anisotropy. The latter two seismological features have been taken to mark the northern limit of Indian mantle lithosphere thrust beneath southern Tibet. On the basis of our electrical model, we speculate that (1) the resistive upper crustal root beneath the Neogene Lunpola and Duba basins was produced by crustal shortening localized along the northern edge of the Lhasa terrane; (2) the low midcrustal resistivity beneath the BNS reflects enhanced Neogene melting and/or metamorphic dewatering of relatively fertile subduction zone complex rocks; (3) observed steep upper crustal low-resistivity anomalies are produced by hydrothermal fluids within active faults localized within and adjacent to the BNS; and (4) these strike-slip and extensional fault arrays are surface manifestations of lithosphere-penetrating shear localized along the northern edge of the underthrust Indian plate.

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Section: Magnetotelluric Methods and Prior Tibetan Mt Experimentsmentioning

confidence: 99%

Structure of the crust in the vicinity of the Banggong‐Nujiang suture in central Tibet from INDEPTH magnetotelluric data

et al. 2005

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“…Increase in porosity, salinity and amount of conducting minerals, raises the ionic conductivity of rocks [19]. Hydrothermal alteration of rocks into clay reduces their resistivity by increasing their bulk conductivity [13,20,21] . The presence of conductive luids in a rock raise the rock bulk conductivity [22].…”

Section: Electrical Conductivity Of Rocksmentioning

confidence: 99%

“…The latter would rule out the fact such near-surface formations contain a luid, and so it's only weathering products that can account for a low resistivity anomaly in this case. Clay-rich alteration products are electrically conductive and thus have an anomalous negative impact on the bulk resistivity on of rocks that host them [13,20,21]. Additionally, clay-rich rocks have resistivity values less than 100 Ohmm [22].…”

Section: ) Reduced Resistivity Between 1000m and 2000mmentioning

confidence: 99%

Geothermal reservoir prediction using electrical resistivity maps: A case study of Lili Sepporaki Indonesia

2019

J. appl. phys. sci.

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The objective of this study is to predict the location of the geothermal reservoir through interpretation of Magnetotelluric depth-resistivity maps, with reference to Lili-Sepporaki geothermal area. Lili-Sepporaki is a nonmagmatic prospect located in Polewali Mandar, Western Sulawesi-Indonesia. The study area is dominated by andesitic to trachytic to trachytic tertiary volcanic products. The only thermal manifestations in the area are the hot springs and rock alterations. Previous geochemical studies found out the hot spring water has temperature of 98 o C and the reservoir temperature of 190 o C. A big portion of the surface rocks are weathered and hydrothermally altered owing to indings from magnetic and Bouguer gravity surveys. This research utilized two-dimensional magnetotellurics data to locate resistivity anomalies in the subsurface. MT data was processed using SSMT2000 and MTEditor software programs while WinGLink software was used in the interpretation of the data. Four resistivity maps were obtained, each corresponding to one of the depths: 500 m; 1000 m; 1500 m; and 2000 m. There is a general sharp reduction in resistivity as opposed to the conventional resistivity of fresh igneous rocks. Analysis shows that the reservoir appears between depths of 1000 m and 2000 in different parts of the survey area, with prospect boundaries located in the South, South West and South East. A three-dimensional MT data analysis and exploration drilling are recommendable in order to get a detailed geothermal model.

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“…The Los Humeros field has been generating electricity since the early ninety´s; nowadays it is producing close to 100 MW, Electrical resistivity is known to be an important physical parameter in the exploration and characterization of geothermal fields. Multiple examples exist of applying resistivity and electromagnetic methods to geothermal systems (Berktold, 1983;Martínez-García, 1992;Spichak and Manzella, 2009;Muñoz, 2014). In this work we analyze the shallow electrical resistivity of Los Humeros geothermal field deduced from more than 600 resistivity and electromagnetic soundings to explore what we can learn on the geothermal reservoir with the analysis of the shallow structure.…”

Section: Introductionmentioning

confidence: 99%

Seal Cap Resistivity Structure of Los Humeros Geothermal Field from Direct Current and Transient Electromagnetic Soundings

2022

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Los métodos geofísicos dan información importante en la exploración de recursos geotérmicos. En este trabajo buscamos pistas de la presencia de un yacimiento geotérmico conocido (Los Humeros, México) en la estructura somera de la resistividad eléctrica. Interpretamos cerca de 410 sondeos eléctricos verticales (SEV) y 230 sondeos electromagnéticos transitorios (TEM) que dan información de la resistividad eléctrica hasta profundidades de 1 km, alcanzándose en algunos sitios hasta 2 km.La estructura vertical de la resistividad generalmente consiste de una secuencia resistivo-conductor-resistivo. El rasgo más importante es la unidad conductora, conocida como el casquete de arcillas, asociado con arcillas de alteración hidrotermal arriba del yacimiento geotérmico. Esta unidad sufre de un problema de equivalencia, donde no se pueden determinar por separado su resistividad de su espesor. Sin embargo, las temperaturas de los pozos y las arcillas de alteración asociadas ayudan a constreñir este problema. En varias zonas de la unidad resistiva somera encontramos resistividades bajas que podrían representar zonas de recarga donde roca fracturada permite la infiltración de agua meteórica. El casquete de arcillas no solo se presenta sobre el yacimiento, sino que tiene una presencia regional. Sin embargo, sobre el reservorio esta unidad tiene una mayor conductancia y su cima está más somera. Los pocos lugares donde los sondeos eléctricos alcanzaron profundidades del yacimiento con resistividades bien resueltas dan una resistividad media de 118 ohm▪m, sin poder diferenciar estadísticamente las zonas productoras de las no productoras. Esta resistividad está dentro del rango de valores encontrados en otras zonas geotérmicas del mundo.

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Electromagnetic induction in geothermal fields and volcanic belts

Cited by 13 publications

References 44 publications

Structure of the crust in the vicinity of the Banggong‐Nujiang suture in central Tibet from INDEPTH magnetotelluric data

Structure of the crust in the vicinity of the Banggong‐Nujiang suture in central Tibet from INDEPTH magnetotelluric data

Geothermal reservoir prediction using electrical resistivity maps: A case study of Lili Sepporaki Indonesia

Seal Cap Resistivity Structure of Los Humeros Geothermal Field from Direct Current and Transient Electromagnetic Soundings

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