17:15 〜 19:15
[SEM15-P13] Three-dimensional resistivity structure in the focal region of the 2000 Western Tottori Earthquake
キーワード：内陸地震、MT法、3次元比抵抗構造
We present the resistivity structure around the focal region of the 2000 Western Tottori Earthquake (M7.3) to investigate the relationship between the mainshock rupture and the resistivity structure.
The Western Tottori Earthquake occurred on October 6, 2000, in an area without surface faulting. Deep low-frequency earthquakes were observed approximately 8 km west of the epicenter at depths of around 30 km. Umeda et al., 2011 (JGR) conducted broadband magnetotelluric (MT) observations around the focal region and performed a three-dimensional analysis using data from 52 sites to explore the relationship between the resistivity structure and deep low-frequency seismic activity. Their study identified an anomalously conductive body extending from the middle crust to the upper mantle on the southwestern side of the mainshock, with deep low-frequency earthquakes occurring at its edge. However, they did not examine the relationship between the resistivity structure and the mainshock rupture.
Aizawa et al., 2021 (EPS) suggested a connection between resistivity structure and major earthquake rupture in the focal region of the 2016 Kumamoto Earthquake. They suggested that a large earthquake initiates from the outer edge of a low-resistivity zone and is arrested by another low-resistivity zone. This raises the possibility that resistivity structure could be used to assess the potential for significant earthquakes, even in areas without active surface faults.
To obtain a more detailed resistivity structure, we conducted additional observations at 35 sites between October and December 2024, including 21 telluric-only sites. For our three-dimensional resistivity analysis, we utilized MT data from 52 sites used in Umeda et al., 2011, 12 sites observed in 2001 by Kyoto University and Tottori University, and the newly added 35 sites.
For the analysis, we employed the FEMTIC code (Usui, 2015 GJI; Usui et al., 2017 GJI) for 3-D inversion, using full components of the impedance tensor and tipper as input data. The inversion accounted for topography, the sea, and two lakes (Nakaumi and Lake Shinji). As a result, we identified a low-resistivity zone directly beneath the mainshock hypocenter. We discuss the relationship between this resistivity structure and the slip distribution of the mainshock or the aftershock distribution.
The Western Tottori Earthquake occurred on October 6, 2000, in an area without surface faulting. Deep low-frequency earthquakes were observed approximately 8 km west of the epicenter at depths of around 30 km. Umeda et al., 2011 (JGR) conducted broadband magnetotelluric (MT) observations around the focal region and performed a three-dimensional analysis using data from 52 sites to explore the relationship between the resistivity structure and deep low-frequency seismic activity. Their study identified an anomalously conductive body extending from the middle crust to the upper mantle on the southwestern side of the mainshock, with deep low-frequency earthquakes occurring at its edge. However, they did not examine the relationship between the resistivity structure and the mainshock rupture.
Aizawa et al., 2021 (EPS) suggested a connection between resistivity structure and major earthquake rupture in the focal region of the 2016 Kumamoto Earthquake. They suggested that a large earthquake initiates from the outer edge of a low-resistivity zone and is arrested by another low-resistivity zone. This raises the possibility that resistivity structure could be used to assess the potential for significant earthquakes, even in areas without active surface faults.
To obtain a more detailed resistivity structure, we conducted additional observations at 35 sites between October and December 2024, including 21 telluric-only sites. For our three-dimensional resistivity analysis, we utilized MT data from 52 sites used in Umeda et al., 2011, 12 sites observed in 2001 by Kyoto University and Tottori University, and the newly added 35 sites.
For the analysis, we employed the FEMTIC code (Usui, 2015 GJI; Usui et al., 2017 GJI) for 3-D inversion, using full components of the impedance tensor and tipper as input data. The inversion accounted for topography, the sea, and two lakes (Nakaumi and Lake Shinji). As a result, we identified a low-resistivity zone directly beneath the mainshock hypocenter. We discuss the relationship between this resistivity structure and the slip distribution of the mainshock or the aftershock distribution.