scholarly journals Three-dimensional inversion of audio-magnetotelluric data acquired from the crater area of Mt. Tokachidake, Japan

2021 ◽  
Vol 73 (1) ◽  
Author(s):  
Ryo Tanaka ◽  
Yusuke Yamaya ◽  
Makoto Tamura ◽  
Takeshi Hashimoto ◽  
Noritoshi Okazaki ◽  
...  
Keyword(s):  
Hydrothermal System ◽  
Hydrothermal Fluid ◽  
Three Dimensional ◽  
Hydrothermal Systems ◽  
High Resistivity ◽  
Water Volume ◽  
Resistivity Structure ◽  
Magnetotelluric Data ◽  
Resistive Layer ◽  
Active Crater

AbstractSubvolcanic hydrothermal systems can lead to hydrothermal eruptions as well as unrest phenomena without an eruptive event. Historical eruptions and recent unrest events, including ground inflation, demagnetization, and a gradual decrease in the plume height, at Mt. Tokachidake, central Hokkaido, Japan, are related to such a subvolcanic hydrothermal system. This study investigates the three-dimensional (3-D) resistivity structure of Mt. Tokachidake to image its subvolcanic hydrothermal system. A 3-D inversion of the magnetotelluric data, acquired at 22 sites around the crater area, was performed while accounting for the topography. Our resistivity model was characterized by a high-resistivity layer at a shallow depth (50–100 m) and two conductors near the active crater and dormant crater. The high-resistivity layer was interpreted to be composed of dense lava, which acts as a caprock surrounding the conductor. The high conductivity beneath the active crater can be explained by the presence of hydrothermal fluid in fractured or leached zones within the low-permeability lava layer, as the sources of ground inflation and demagnetization were identified within the conductive zone immediately beneath the resistive layer. The resistivity structure was used to estimate the volume of hydrothermal fluid within the pore space. The minimum volume of hydrothermal fluid beneath the active crater that can explain the resistivity structure was estimated to be 3 × 106 m3. This estimate is comparable to the water volume that was associated with the long runout and highly fluidized lahar in 1926. The resistivity structure and volume of hydrothermal fluid presented in this study can be used as a reference for further numerical simulations, which aim to reveal the mechanisms of recent unrest events and assess the risk of hazards, such as lahar.

Fluid network framing the hydrothermal system beneath Mt. Erciyes, Central Turkey

2020 ◽  
Author(s):  
Mustafa Karaş ◽  
Serkan Üner ◽  
Sabri Bülent Tank
Keyword(s):  
Electrical Resistivity ◽  
Hydrothermal System ◽  
Magma Mixing ◽  
Current Model ◽  
Wide Band ◽  
Hydrothermal Systems ◽  
Resistivity Structure ◽  
Mixing Processes ◽  
Magnetotelluric Data ◽  
Study Region

<p>Fluid contribution in a tectonic process is a crucial parameter for characterization of its products. In the geophysical point of view, illustrating the electrical resistivity structure of any tectonic system can be used to determine effects of fluid contribution. Magnetotellurics is globally used to decipher characteristics of fault zones, volcanoes and hydrothermal systems which are related to driving tectonic regime in collision and transition zones. Mt. Erciyes, which is the largest composite volcano of the Central Anatolian Volcanic Province in Turkey, developed in two particular stages during the Quaternary. Igneous activities in Koçdağ and New Erciyes stages created a plausible environment to observe dominant calc-alkaline products while alkaline and tholeiitic components are also present in the region. Geochemical evidences offer that fractional crystallization combined with low degree crustal assimilation were experienced during the formation of the volcano in addition to potential magma mixing processes occurred in the magma chambers. As part of NSF-funded Continental Dynamics/Central Anatolian Tectonics Project (CD/CAT), this study aims to investigate electrical resistivity structure beneath Mt. Erciyes by means of three-dimensional modeling of the wide-band magnetotelluric data collected at 48 sounding locations. Current model depicts a high conductivity anomaly beneath Mt. Erciyes, which corresponds to its hydrothermal system and related clay cap. Within Erciyes pull-apart basin, local branches of Ecemiş Fault Zone that possibly reinforced the convenient setting for the upwelling of volcanic materials, bound the interconnected highly conductive zones in shallow depths. Under these circumstances, a complex resistivity distribution arises as a consequence of various electrical transfer mechanisms contemplated for the study region.</p>

scholarly journals Analysis of Hydrothermal Systems Beneath Tayukeng through Long-Term Geochemical Signals of Hydrothermal Fluids in Tatun Volcano Group, Taiwan

2021 ◽  
Vol 18 (14) ◽  
pp. 7411
Author(s):  
Hsin-Fu Yeh ◽  
Hung-Hsiang Hsu
Keyword(s):  
Surface Temperature ◽  
Hydrothermal System ◽  
Hydrothermal Fluid ◽  
Thermal Water ◽  
Hydrothermal Systems ◽  
Hydrothermal Fluids ◽  
Geochemical Variations ◽  
Northern Taiwan

The Tatun Volcano Group (TVG) is located in northern Taiwan and consists of many springs and fumaroles. The Tayukeng (TYK) area is the most active fumarole site in the TVG. In this study, we analyzed the long-term geochemical variations of hydrothermal fluids and proposed a mechanism responsible for the variation in TYK. There are two different aquifers beneath the TYK area: a shallow SO42−-rich aquifer and a deeper aquifer rich in Cl−. TYK thermal water was mainly supplied by the shallow SO42−-rich aquifer; therefore, the thermal water showed high SO42− concentrations. After 2015, the inflow of deep thermal water increased, causing the Cl− concentrations of the TYK to increase. Notably, the inferred reservoir temperatures based on quartz geothermometry increased; however, the surface temperature of the spring decreased. We inferred that the enthalpy was lost during transportation to the surface. Therefore, the surface temperature of the spring does not increase with an increased inflow of deep hydrothermal fluid. The results can serve as a reference for understanding the complex evolution of the magma-hydrothermal system in the TVG.

scholarly journals Electrical resistivity modeling around the Hidaka collision zone, northern Japan: regional structural background of the 2018 Hokkaido Eastern Iburi earthquake (Mw 6.6)

2019 ◽  
Vol 71 (1) ◽  
Author(s):  
Hiroshi Ichihara ◽  
Toru Mogi ◽  
Hideyuki Satoh ◽  
Yusuke Yamaya
Keyword(s):  
Three Dimensional ◽  
High Resistivity ◽  
Reverse Fault ◽  
Magnetotelluric Data ◽  
Epicentral Area ◽  
Collision Zone ◽  
Conductive Zone ◽  
Significant Area ◽  
Resistivity Model ◽  
Hidaka Collision Zone

Abstract The Hidaka collision zone, the collision boundary between the NE Japan and Kurile arcs, is known to be an ideal region to study the evolution of island arcs. The hypocenter of the 2018 Hokkaido Eastern Iburi earthquake (Mw 6.6) in the western part of the Hidaka collision zone was unusually deep for an inland earthquake, and the reverse fault that caused the earthquake has an uncharacteristically steep dip. In this study, we used three-dimensional inversion to reanalyze broadband magnetotelluric data acquired in the collision zone. The inverted resistivity model showed a significant area of high resistivity around the center of the collision boundary. We also identified a conductive zone beneath an area of serpentinite mélange in a zone of high P–T metamorphic rocks west of the high-resistivity zone. The conductive zone possibly reflects areas rich in pore fluids related to the formation and elevation of the serpentinites. Sensitivity tests indicated the need for additional magnetotelluric survey data to delineate the resistivity distribution around the epicentral area of the 2018 earthquake although the resistivity model showed a conductive zone in this area.

Three-dimensional resistivity structure in the hydrothermal system beneath Ganzi Basin, eastern margin of Tibetan Plateau

Geothermics ◽  
2021 ◽  
Vol 93 ◽  
pp. 102062
Author(s):  
Yuanzhi Cheng ◽  
Zhonghe Pang ◽  
Qingyun Di ◽  
Xiaobin Chen ◽  
Yanlong Kong
Keyword(s):  
Tibetan Plateau ◽  
Hydrothermal System ◽  
Three Dimensional ◽  
Resistivity Structure ◽  
Eastern Margin

scholarly journals Mapeo tridimensional del valor b en el Volcán Nevado del Ruíz, Colombia [3D mapping of b-value at Nevado del Ruiz Volcano, Colombia]

2014 ◽  
Author(s):  
John Makario LONDOÑO BONILLA ◽  
Sandra Patricia RODRÍGUEZ G.
Keyword(s):  
Hydrothermal System ◽  
Three Dimensional ◽  
B Value ◽  
3D Mapping ◽  
Magnitude Distribution ◽  
High B Value ◽  
Three Dimensional Mapping ◽  
Active Crater ◽  
Frequency Magnitude Distribution ◽  
Frequency Magnitude

Resumen Se realizó un mapeo tridimensional del valor-b para la sismicidad volcano-tectónica del Volcán Nevado del Ruiz (VNR) para el período comprendido entre 1985 y 2002.Se pudieron definir cuatro zonas anómalas (altos valores) de b en el VNR, localizadas, unaal oeste del cráter activo cerca al cráter la Olleta (b=1.3-1.8), asociada con un sistema hidrotermal en superficie (z=1Km) y una zona de alimentación magmática en profundidad (z=6Km); otra zona (b=1.4),ubicada bajo el cráter activo Arenas (z=1Km) asociada con un sector de acumulación de vapor y fluidos que harían parte del sistema hidrotermal del VNR; otra zona (b=1.7), localizada al sur del cráter activo (Z=6Km) asociada posiblemente a la localización de una de las cámaras magmáticas del VNR; y otra zona (b=1.7), ubicada al NE del cráter activo (z=3Km) cerca al cráter la Piraña, asociada también a una zona de alimentación magmática. Estas zonas son coincidentes con las halladas en otros estudios usando tomografía sísmica para el VNR, al igual que con estudios petrológicos y geoquímicos. Palabras clave:valor-b, mapeo 3D, sismicidad, distribución frecuencia-magnitud de sismos   Abstract Three-dimensional mapping of b-value (frequency-magnitude distribution) was done for Nevado del Ruiz Volcano (NRV), Colombia for the period 1985-2002.Four high b-value zones were detected. The first zone (b=1.3 -1.8), located to the west of the active crater (Arenas), close to the Olleta crater. This zone was associated with a hydrothermal system at surface (z=1Km),andwith a zone ofmagma supply atdepth(z >6Km). The second zone (b=1.4), located beneath the Arenas crater (z=1Km) was associated with a zone of fluid and vapor accumulation related with the hydrothermal system of NRV. The third zone (b=1.7), located to the south of Arenas crater (z=6Km) was associated with one of the magmatic chambers of NRV; and the forth zone (b=1.7), located to theNE of the Areas crater (z=3Km) near to the Piraña crater, was associated with another magma supply zone. Those zones are in agreement with studies of seismic tomography, geochemistry and petrology done previouslyat NRV. Keywords: b-value, 3d mapping, seismicity, earthquake frequency-magnitude distribution

Three-dimensional inversion of controlled-source audio-frequency magnetotelluric data based on unstructured finite-element method

2020 ◽  
Vol 17 (3) ◽  
pp. 349-360
Author(s):  
Xiang-Zhong Chen ◽  
Yun-He Liu ◽  
Chang-Chun Yin ◽  
Chang-Kai Qiu ◽  
Jie Zhang ◽  
...  
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Three Dimensional ◽  
Audio Frequency ◽  
Magnetotelluric Data ◽  
Controlled Source ◽  
Element Method

scholarly journals Correcting for Static Shift of Magnetotelluric Data with Airborne Electromagnetic Measurements: A Case Study from Rathlin Basin, Northern Ireland

2016 ◽  
Author(s):  
Robert Delhaye ◽  
Volker Rath ◽  
Alan G. Jones ◽  
Mark R. Muller ◽  
Derek Reay
Keyword(s):  
Distortion Correction ◽  
Vertical Scaling ◽  
Spatial Density ◽  
Target Area ◽  
Resistivity Structure ◽  
Static Shift ◽  
Magnetotelluric Data ◽  
Archie’S Law ◽  
Order Of Magnitude ◽  
Resistivity Variation

Abstract. Galvanic distortions of magnetotelluric (MT) data, such as the static shift effect, are a known problem that can lead to incorrect estimation of resistivities and erroneous modelling of geometries with resulting misinterpretation of subsurface electrical resistivity structure. A wide variety of approaches have been proposed to account for these galvanic distortions, some depending on the target area, with varying degrees of success. The natural laboratory for our study is a hydraulically permeable volume of conductive sediment at depth, the internal resistivity structure of which can be used to estimate reservoir viability for geothermal purposes, however static shift correction is required in order to ensure robust and precise modelling accuracy. We propose a method employing frequency–domain electromagnetic data for static shift correction, which in our case are regionally available with high spatial density. The spatial distributions of the derived static shift corrections are analysed and applied to the uncorrected MT data prior to inversion. Two comparative inversion models are derived, one with and one without static shift corrections, with instructive results. As expected from the one–dimensional analogy of static shift correction, at shallow model depths, where the structure is controlled by a single local MT site, the correction of static shift effects leads to vertical scaling of resistivity-thickness products in the model, with the corrected model showing improved correlation to existing borehole wireline resistivity data. In turn, as these vertical scalings are effectively independent of adjacent sites, lateral resistivity distributions are also affected, with up to half a decade of resistivity variation between the models estimated at depths down to 2000 m. Simple estimation of differences in bulk porosity, derived using Archie’s Law, between the two models reinforces our conclusion that the sub–order of magnitude resistivity contrasts induced by correction of static shifts correspond to similar contrasts in estimated porosities, and hence, for purposes of reservoir investigation or similar cases requiring accurate absolute resistivity estimates, galvanic distortion correction, especially static shift correction, is essential.

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