17:15 〜 18:45
[SEM12-P16] 中国・四国地方の基盤的比抵抗構造調査(2023年度)
キーワード：基盤的比抵抗構造調査、中国四国地方、3次元比抵抗構造
The purpose of this study is to investigate the spatial and structural heterogeneity of the crust and upper mantle beneath Chugoku and Shikoku regions by conducting MT investigations to contribute to the mitigation of disasters due to earthquakes and volcanic eruptions.
So far, our research group has shown a close relationship between resistivity structure and seismic activity in the San'in and Shikoku regions. For example, in the eastern part of the San'in region, there are large earthquake occurrence areas and belt-shaped seismic activities along the coast of the Sea of Japan, including the Shikano-Yoshioka fault, which is the surface fault of the Tottori earthquake (1943, M = 7.2). In the Shikoku region, the survey results mainly in the outer zone of Shikoku indicate the presence of remarkable conductive regions in the upper crust, and that it is clearly related to aseismic regions in the central and western area of the outer zone. If an inland earthquake is caused by local stress concentration caused by an inhomogeneous structure directly under the seismic activity zone (Iio, 2009), it is important to carefully examine the inhomogeneous structure and consider the relation of seismic activity and stress concentration / relaxation.
We started a 3 D resistivity structure analysis using the MT data from the fundamental investigations in Chugoku and Shikoku regions. We will report on the findings obtained as a result of structural analysis for each region, including 1) the eastern Tottori to midwestern region, 2) the central Shikoku region, and 3) the eastern part of Shimane region.
The preliminary 3 D analysis shows several results. First, it confirmed the relationship between seismic activity and resistivity structure previously shown in the San'in and Shikoku regions through 2D analysis. Secondly, it estimates the spatial extent of the deep extension of the low resistivity region that exists beneath the crustal earthquake in the San'in region, which has not been discussed so far. It is particularly interesting that the northern region of the low resistivity region is spatially related to the low-frequency earthquake region, and that seismic activity and volcanoes in the San'in region exist in the northern extension. The results obtained from the first 3 D resistivity structure analysis in these regions is essential data for a more reliable understanding of seismic activity and volcanic area in these regions.
We received support from the Ministry of Education, Culture, Sports, Science and Technology for the Earthquake and Volcano Observation Research Program to contribute to the mitigation of disasters.
So far, our research group has shown a close relationship between resistivity structure and seismic activity in the San'in and Shikoku regions. For example, in the eastern part of the San'in region, there are large earthquake occurrence areas and belt-shaped seismic activities along the coast of the Sea of Japan, including the Shikano-Yoshioka fault, which is the surface fault of the Tottori earthquake (1943, M = 7.2). In the Shikoku region, the survey results mainly in the outer zone of Shikoku indicate the presence of remarkable conductive regions in the upper crust, and that it is clearly related to aseismic regions in the central and western area of the outer zone. If an inland earthquake is caused by local stress concentration caused by an inhomogeneous structure directly under the seismic activity zone (Iio, 2009), it is important to carefully examine the inhomogeneous structure and consider the relation of seismic activity and stress concentration / relaxation.
We started a 3 D resistivity structure analysis using the MT data from the fundamental investigations in Chugoku and Shikoku regions. We will report on the findings obtained as a result of structural analysis for each region, including 1) the eastern Tottori to midwestern region, 2) the central Shikoku region, and 3) the eastern part of Shimane region.
The preliminary 3 D analysis shows several results. First, it confirmed the relationship between seismic activity and resistivity structure previously shown in the San'in and Shikoku regions through 2D analysis. Secondly, it estimates the spatial extent of the deep extension of the low resistivity region that exists beneath the crustal earthquake in the San'in region, which has not been discussed so far. It is particularly interesting that the northern region of the low resistivity region is spatially related to the low-frequency earthquake region, and that seismic activity and volcanoes in the San'in region exist in the northern extension. The results obtained from the first 3 D resistivity structure analysis in these regions is essential data for a more reliable understanding of seismic activity and volcanic area in these regions.
We received support from the Ministry of Education, Culture, Sports, Science and Technology for the Earthquake and Volcano Observation Research Program to contribute to the mitigation of disasters.