3:00 PM - 3:15 PM
[SVC31-16] Resistivity structure around Shiga Volcano and Takayama Village
Keywords:Shiga Volcano, Magnetotellulic, Resistivity structure
Shiga Volcano is a Quaternary volcano located in the northeastern part of Nagano Prefecture, near the border with Gunma Prefecture. It consists of two andesitic volcanoes, Mt. Shiga and Mt. Hachiyama. Shiga Volcano is believed to have been active from 25 ka to 5 ka (Kaneko et al., 1991), and therefore, is not currently designated as an active volcano. However, recent geological studies in Mt. Shiga suggest possible lava flows in the Holocene (Oikawa, 2019) and possible phreatic eruptions within the last 500 years (Murakami and Ishizaki, 2020). The three-dimensional resistivity structure of the Kusatsu-ShiraneVolcano, located ~6 km south-southeast, also suggests that the Shiga Volcano can have a common deep-seated magma with the Kusatsu-Shirane Volcano (Matsunaga et al., 2022).
In this study, we conducted magnetotelluric (MT) observation for the purpose of clarifying the subsurface structure of the Shiga Volcano and investigating the relationship with the magma-hydrothermal system of the Kusatsu-Shirane Volcano. Observations were conducted from August to October 2022 at a total of 22 sites, 16 sitesaround the Shiga Volcano and 6 sites in Takayama Villagewithin an area of approximately 7 km north-south by 7 km east-west.
Due to the steep topography of this area, only two horizontal components of the electric field were measuredin the summit area and in places with poor access. The analysis of the data for those sites was carried out using the magnetic field data measured at the nearby site. In the analysis, the MT response functions from 2 to 10,000 Hz were obtained by the mutual remote-reference technique, which was generally of good quality. The obtained MT responses were analyzed using the inversion code utilizing an unstructured tetrahedral mesh to represent the relatively accurate topographic undulations developed by Usui (2015), and the three-dimensional resistivity structure model was estimated.
In this presentation, we discuss the inferred heterogeneous resistivity structures down to a depth of ~1 km.
In this study, we conducted magnetotelluric (MT) observation for the purpose of clarifying the subsurface structure of the Shiga Volcano and investigating the relationship with the magma-hydrothermal system of the Kusatsu-Shirane Volcano. Observations were conducted from August to October 2022 at a total of 22 sites, 16 sitesaround the Shiga Volcano and 6 sites in Takayama Villagewithin an area of approximately 7 km north-south by 7 km east-west.
Due to the steep topography of this area, only two horizontal components of the electric field were measuredin the summit area and in places with poor access. The analysis of the data for those sites was carried out using the magnetic field data measured at the nearby site. In the analysis, the MT response functions from 2 to 10,000 Hz were obtained by the mutual remote-reference technique, which was generally of good quality. The obtained MT responses were analyzed using the inversion code utilizing an unstructured tetrahedral mesh to represent the relatively accurate topographic undulations developed by Usui (2015), and the three-dimensional resistivity structure model was estimated.
In this presentation, we discuss the inferred heterogeneous resistivity structures down to a depth of ~1 km.