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[SEM14-01] Imaging the magma plumbing system of Mt. Meakandake volcano based on broadband magnetotellurics and three-dimensional resistivity modelling
Keywords:magnetotelluric, Meakandake, resistivity, magma plumbing system
This study reports an updated resistivity model for Mt. Meakandake, one of the active volcanoes in eastern Hokkaido. On the northeastern foot of the volcano, a remarkable ground inflation was observed during the period from 2016 to 2017 (Geospatial Information Authority of Japan, 2018). We modelled the resistivity structure targeting at the inflation source, based on the BBMT data in 2018 and 2019 (Inoue et al., 2020; SGEPSS) and the AMT/BBMT data in 2010 recorded on the south shore of Lake Akan (Mogi et al., 2011). Our previous resistivity model has imaged a distinct conductive column C1 (about 1-10 Ωm) extending from 0.5 km BSL just below the summit to a deeper part of Mt. Meakandake. However, the geometry and spatial extent of C1 has not been well constrained by the lack of MT observation sites. Therefore, in the fall of 2020, we deployed six additional BBMT sites in the summit area and the western foot of the volcano to achieve a better constraint on C1.
We acquired the time series of five components (2E+3H) for about seven days using the ADU07e system (Metronix Ltd.) for the three sites in the western foot of Mt. Meakandake. On the summit area, we measured only 2E using the Elog-dual recorder (NT System Design Ltd.). In calculating the response functions, we used the BIRRP (Chave and Thomson, 2004) and applied the remote reference processing (Gamble et al., 1997) using the data at the continuous station in Yamagata Prefecture (about 700 km southwest from our study area) that was provided by Geothermal Energy Research & Development Co., Ltd.
The overall characteristics of the apparent resistivity and phase curves suggested the structure of roughly middle–low–high resistivity from the surface toward deeper part. Some of the additional sites showed anomalous phases in Zyx component in a period range over 1000 s. The induction vectors at the western sites directed roughly to Mt. Fuppushidake and east, in constant to those at the sites in the northern to eastern foot of the volcano, pointing to an opposite direction. It suggested another conductive body beneath Mt. Fuppushidake in the north side of Mt. Meakandake.
We performed a provisional inversion using the previous 3D resistivity model (Inoue et al., 2020; SGEPSS) as a starting model and examined how the additional data would affect the result. We inverted the full impedance and tipper of 39 existing sites and six additional sites using by the ModEM (Egbert and Kelbert, 2012; Kelbert et al., 2014).
It resulted in a final RMS misfit about 2.8 for the input data with an error floor of 5 %, comparable to the final misfit of the previous inversion modelling by Inoue et al (2020; SGEPSS). Responses at the additional sites were also well reproduced by this provisional inversion in which no significant modification was made from the previous modelling. The additional data acquisition and modelling in this study confirmed that the C1 was meaningful down to about 30 km BSL. We consider it may be a part of the magma plumbing system. As a next step, we plan to discuss the physical state in the C1 based on the estimation of rock properties such as melt fraction.
Acknowledgments: This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under it’s the Second Earthquake and Volcano Hazards Observation and Research Program (Earthquake and Volcano Hazard Reduction Research).
We acquired the time series of five components (2E+3H) for about seven days using the ADU07e system (Metronix Ltd.) for the three sites in the western foot of Mt. Meakandake. On the summit area, we measured only 2E using the Elog-dual recorder (NT System Design Ltd.). In calculating the response functions, we used the BIRRP (Chave and Thomson, 2004) and applied the remote reference processing (Gamble et al., 1997) using the data at the continuous station in Yamagata Prefecture (about 700 km southwest from our study area) that was provided by Geothermal Energy Research & Development Co., Ltd.
The overall characteristics of the apparent resistivity and phase curves suggested the structure of roughly middle–low–high resistivity from the surface toward deeper part. Some of the additional sites showed anomalous phases in Zyx component in a period range over 1000 s. The induction vectors at the western sites directed roughly to Mt. Fuppushidake and east, in constant to those at the sites in the northern to eastern foot of the volcano, pointing to an opposite direction. It suggested another conductive body beneath Mt. Fuppushidake in the north side of Mt. Meakandake.
We performed a provisional inversion using the previous 3D resistivity model (Inoue et al., 2020; SGEPSS) as a starting model and examined how the additional data would affect the result. We inverted the full impedance and tipper of 39 existing sites and six additional sites using by the ModEM (Egbert and Kelbert, 2012; Kelbert et al., 2014).
It resulted in a final RMS misfit about 2.8 for the input data with an error floor of 5 %, comparable to the final misfit of the previous inversion modelling by Inoue et al (2020; SGEPSS). Responses at the additional sites were also well reproduced by this provisional inversion in which no significant modification was made from the previous modelling. The additional data acquisition and modelling in this study confirmed that the C1 was meaningful down to about 30 km BSL. We consider it may be a part of the magma plumbing system. As a next step, we plan to discuss the physical state in the C1 based on the estimation of rock properties such as melt fraction.
Acknowledgments: This study was supported by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan, under it’s the Second Earthquake and Volcano Hazards Observation and Research Program (Earthquake and Volcano Hazard Reduction Research).