17:15 〜 19:15
[SVC32-P19] Three-dimensional resistivity structure of Hakone volcano, Japan.
キーワード：箱根火山、MT法、3次元比抵抗構造
We present a preliminary three-dimensional resistivity structure of Hakone volcano, located approximately 100 km southwest of Tokyo. This volcano experienced volcanic unrest in 2015, including small phreatic eruptions, seismic swarm activity, and ground deformation. Previous studies have provided high-resolution seismic velocity structures to a depth of 30 km, but resistivity structures have only been estimated to a depth of 3km (Yoshimura et al., 2018 EPS). Recent studies highlighted discrepancies between low-resistivity and low-velocity anomalies at other volcanoes, indicating the challenges in interpreting volcano structures based solely on resistivity. Our ultimate goal is to better understand volcanic fluid pathways by integrating these complementary datasets.
We conducted a wide-band Magneto-telluric survey in and around Hakone volcano, deploying 41-observation points during September and October 2023. We recorded Magneto-telluric (MT) data continuously for over a month, with a sampling rate of 32 Hz during the day and 1024 Hz at night (Japan Standard Time 2:00-3:00) to estimate good quality MT response functions in an area of high EM noise due to dense population, high-voltage power lines, and Direct Current electric railways. In calculating MT response functions, we used BIRRP program (Chave and Thomson, 2004) with remote-reference processing using geomagnetic data collected 850 km west of Hakone volcano. As a result, we obtained moderate-quality MT response functions in the periods range of 0.005 s to 1000 s at 20 of 41 sites.
In this study, we estimated the preliminary 3-D resistivity structure using hexahedral mesh and the FEMTIC code (Usui, 2015 GJI; Usui et al., 2017 GJI, 2024 JGR). The input data consists of the full components of impedance tensor and tippers. In addition to the broad-band MT data collected at 41 sites in 2023, we also used AMT data from 65 sites used in Yoshimura et al., 2018 EPS. The imaged shallow resistivity structure is similar to that of Yoshimura et al., (2018), with a bell-shaped low resistivity layer beneath the Owakudani geothermal zone. At depth greater than 4 km, the resistivity structure is not fully constrained from the dataset. Therefore, we need to improve the quality of MT response function of broad-band MT sites acquired in 2023.
We conducted a wide-band Magneto-telluric survey in and around Hakone volcano, deploying 41-observation points during September and October 2023. We recorded Magneto-telluric (MT) data continuously for over a month, with a sampling rate of 32 Hz during the day and 1024 Hz at night (Japan Standard Time 2:00-3:00) to estimate good quality MT response functions in an area of high EM noise due to dense population, high-voltage power lines, and Direct Current electric railways. In calculating MT response functions, we used BIRRP program (Chave and Thomson, 2004) with remote-reference processing using geomagnetic data collected 850 km west of Hakone volcano. As a result, we obtained moderate-quality MT response functions in the periods range of 0.005 s to 1000 s at 20 of 41 sites.
In this study, we estimated the preliminary 3-D resistivity structure using hexahedral mesh and the FEMTIC code (Usui, 2015 GJI; Usui et al., 2017 GJI, 2024 JGR). The input data consists of the full components of impedance tensor and tippers. In addition to the broad-band MT data collected at 41 sites in 2023, we also used AMT data from 65 sites used in Yoshimura et al., 2018 EPS. The imaged shallow resistivity structure is similar to that of Yoshimura et al., (2018), with a bell-shaped low resistivity layer beneath the Owakudani geothermal zone. At depth greater than 4 km, the resistivity structure is not fully constrained from the dataset. Therefore, we need to improve the quality of MT response function of broad-band MT sites acquired in 2023.