5:15 PM - 6:30 PM
[SSS05-P05] Evaluation of inland seismic potential in southwest Japan using GNSS data and seismic catalog
Keywords:seismic potential, GNSS observation, seismic catalog, seismic moment
Major earthquakes have repeatedly caused massive damage in Japan. The Headquarters for Earthquake Research Promotion (HERP) evaluates the seismic potential for major earthquakes. Although the HERP had only assessed damaging earthquakes at major active faults, several major earthquakes occurred along non-target faults recently. Against this background, some previous research estimated inland seismic potential regionally based on strain rates estimated from GNSS observation and Japan Metrological Agency (JMA) seismic catalog. However, they ignore the effects of interplate coupling and postseismic deformations on strain rates (Takahashi & Shinohara, 2015), and use a relatively shorter period of seismic catalog for calculating the seismic momentˈs release rate (Kimura et al., 2018). We evaluated inland seismic potential at each crustal block of southwest Japan using internal strain rates at each crustal block and a relatively longer seismic catalog.
Inland earthquakes release accumulated internal strain in the crustal block. Based on this relation, we focused on accumulation and release rates of the seismic moment at each crustal block, and evaluated inland seismic potential using the balance between both rates. To evaluate the seismic potential, we used the crustal block model and internal strain rates at each crustal block (Kimura et al., 2018), and seismic catalogs by JMA and Utsu (1982, 1985). The seismic momentˈs accumulation rate is equivalent to the average seismic moment rate due to plate motion and interaction between crustal blocks It is calculated from internal strain rates, thickness of seismogenic layer (D90 in this research), and the equation proposed by Savage & Simpson (1997). On the other hand, the seismic momentˈs release rate corresponds to the released average seismic moment rate due to earthquakes. It is obtained from seismic moment integration assuming that inland earthquakes occur according to cumulative GR-law. Then, we regarded the difference of accumulation and release rates as the energy released by future earthquakes. The evaluated inland seismic potential in 30 years assumed the occurrence of Mw7.0 earthquakes using the Poisson process.
We evaluated inland seismic potential at six crustal blocks. In Kinki and Setouchi blocks, the estimated seismic potentials from combined geodetic data are 2.16±0.01% and 9.07±0.25%, respectively. We compared the results with the seismicity at each crustal block. As a result, the seismic potentials estimated from the seismicity are 0.08±0.001% and 3.25±0.02%, respectively, and are close to the seismic potentials from combined geodetic data. Therefore, the estimated seismic potentials are consistent with the seismicity. In the Forearc block, while the estimated seismic potential from combined geodetic data is 62.06±0.16%, the seismic potential from the seismicity is 3.69±0.02%. It is significantly smaller than the estimated seismic potential from combined geodetic data. However, since internal strain rates at the Forearc block are relatively larger than other crustal blocks, this discrepancy reflects the relatively higher risk for major earthquakes. In the Okinawa block, the estimated seismic potential from combined geodetic data is 99.87±0.002%. The crustal block has a significantly wide area covering from Kagoshima to Taiwan and significantly large internal strain rates due to a single crustal block, including the interaction between crustal blocks. Therefore, the significantly high seismic potential may reflect both effects. In the Chubu block and Izu microplate, the seismic potentials from combined geodetic data cannot be evaluated because the release rates are larger than the accumulation rates. In both crustal blocks, the release rates may be overestimated due to the various effects of active volcanoes. In the future, we need to improve our methods, such as removing the earthquakes near active volcanoes and the boundaries of crustal blocks.
Inland earthquakes release accumulated internal strain in the crustal block. Based on this relation, we focused on accumulation and release rates of the seismic moment at each crustal block, and evaluated inland seismic potential using the balance between both rates. To evaluate the seismic potential, we used the crustal block model and internal strain rates at each crustal block (Kimura et al., 2018), and seismic catalogs by JMA and Utsu (1982, 1985). The seismic momentˈs accumulation rate is equivalent to the average seismic moment rate due to plate motion and interaction between crustal blocks It is calculated from internal strain rates, thickness of seismogenic layer (D90 in this research), and the equation proposed by Savage & Simpson (1997). On the other hand, the seismic momentˈs release rate corresponds to the released average seismic moment rate due to earthquakes. It is obtained from seismic moment integration assuming that inland earthquakes occur according to cumulative GR-law. Then, we regarded the difference of accumulation and release rates as the energy released by future earthquakes. The evaluated inland seismic potential in 30 years assumed the occurrence of Mw7.0 earthquakes using the Poisson process.
We evaluated inland seismic potential at six crustal blocks. In Kinki and Setouchi blocks, the estimated seismic potentials from combined geodetic data are 2.16±0.01% and 9.07±0.25%, respectively. We compared the results with the seismicity at each crustal block. As a result, the seismic potentials estimated from the seismicity are 0.08±0.001% and 3.25±0.02%, respectively, and are close to the seismic potentials from combined geodetic data. Therefore, the estimated seismic potentials are consistent with the seismicity. In the Forearc block, while the estimated seismic potential from combined geodetic data is 62.06±0.16%, the seismic potential from the seismicity is 3.69±0.02%. It is significantly smaller than the estimated seismic potential from combined geodetic data. However, since internal strain rates at the Forearc block are relatively larger than other crustal blocks, this discrepancy reflects the relatively higher risk for major earthquakes. In the Okinawa block, the estimated seismic potential from combined geodetic data is 99.87±0.002%. The crustal block has a significantly wide area covering from Kagoshima to Taiwan and significantly large internal strain rates due to a single crustal block, including the interaction between crustal blocks. Therefore, the significantly high seismic potential may reflect both effects. In the Chubu block and Izu microplate, the seismic potentials from combined geodetic data cannot be evaluated because the release rates are larger than the accumulation rates. In both crustal blocks, the release rates may be overestimated due to the various effects of active volcanoes. In the future, we need to improve our methods, such as removing the earthquakes near active volcanoes and the boundaries of crustal blocks.