5:15 PM - 7:15 PM
[SEM15-P12] Analysis of Long-Period MT Data and Wideband MT Data in the Kii Peninsula, Southwestern Japan
Keywords:electrical resistivity structure, Kii Peninsula, Deep Low-Frequency tremor, high-temperature hot springs, Network-MT method
The Kii Peninsula in the forearc region of southwestern Japan has distinct structural and tectonic features due to the subducting Philippine Sea slab. These include high-seismicity, deep low-frequency tremors, and high-temperature hot springs. The Kii Peninsula is key to understanding the relationship between deep fluids and seismic activities.
In my previous research, we analyzed the network-MT data acquired in the Kii Peninsula to estimate a 3-D regional deep resistivity model for the first time. The resultant model seems to be the most reliable as for the deep subsurface structure, which has a complex 3-D nature. The model shows a high-resistivity zone, considered as a Kumano acidic rock body (KAR), beneath the Kii Peninsula and corresponds well with the seismic high-velocity zone and the high-gravity anomaly zone. A low-resistivity region surrounds the high-resistivity region, and a prominent low-resistivity region extends from the top of the slab to the crustal surface. In the model, this correspondence between the resistivity structure and the spatial distribution of the hot springs may explain the fluid contribution in the subsurface of the Kii Peninsula.
The network-MT method (Uyeshima et al., 2001; Uyeshima, 2007) used in this study employs a commercial telephone network to measure voltage differences over long dipole lengths (10 to several tens of kilometers). This method has three advantages over conventional MT methods: wider spatial coverage (covering almost the entire Kii Peninsula), a wider period range (from tens of seconds to 50,000 seconds), and better data quality in terms of a high signal-to-noise ratio and less susceptibility to static effects. However, while the network-MT data had high sensitivity to deep structures, it had low resolution for the middle and upper crust due to the lack of high-frequency data. Additionally, observations were limited to areas with telephone lines, creating some spatial observation gaps. To address these deficiencies, we plan to compile existing conventional MT data and conduct observations to fill the observation gaps in frequency and spatial domain. We analyzed the following data.
・long-period MT data (observed by Ogawa et al., 2017-2018)
・Wide-Band MT data (observed by Yoshimura et al., 2005)
・Wide-Band MT data (new observations in this study)
In this presentation, we show the results of those analyses.
In my previous research, we analyzed the network-MT data acquired in the Kii Peninsula to estimate a 3-D regional deep resistivity model for the first time. The resultant model seems to be the most reliable as for the deep subsurface structure, which has a complex 3-D nature. The model shows a high-resistivity zone, considered as a Kumano acidic rock body (KAR), beneath the Kii Peninsula and corresponds well with the seismic high-velocity zone and the high-gravity anomaly zone. A low-resistivity region surrounds the high-resistivity region, and a prominent low-resistivity region extends from the top of the slab to the crustal surface. In the model, this correspondence between the resistivity structure and the spatial distribution of the hot springs may explain the fluid contribution in the subsurface of the Kii Peninsula.
The network-MT method (Uyeshima et al., 2001; Uyeshima, 2007) used in this study employs a commercial telephone network to measure voltage differences over long dipole lengths (10 to several tens of kilometers). This method has three advantages over conventional MT methods: wider spatial coverage (covering almost the entire Kii Peninsula), a wider period range (from tens of seconds to 50,000 seconds), and better data quality in terms of a high signal-to-noise ratio and less susceptibility to static effects. However, while the network-MT data had high sensitivity to deep structures, it had low resolution for the middle and upper crust due to the lack of high-frequency data. Additionally, observations were limited to areas with telephone lines, creating some spatial observation gaps. To address these deficiencies, we plan to compile existing conventional MT data and conduct observations to fill the observation gaps in frequency and spatial domain. We analyzed the following data.
・long-period MT data (observed by Ogawa et al., 2017-2018)
・Wide-Band MT data (observed by Yoshimura et al., 2005)
・Wide-Band MT data (new observations in this study)
In this presentation, we show the results of those analyses.