11:30 AM - 11:45 AM
[SGD02-09] Evaluation of Inland Seismic Potential in sosuthwest Japan using Geodetic and Seismic Data
Keywords:Inland Seismic Potential, GNSS Observation, Seismic catalog
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 based on strain rates estimated from GNSS observation and Japan Metrological Agency (JMA) seismic catalog. However, they used the GNSS velocity, including the rigid motion of each crustal block and the constant value for some parameters, such as the b-value of the truncated Gutenberg-Richter law (TGR-law) and the maximum magnitude (Nishimura, 2022). So, we evaluated inland seismic potential at a 0.1° square grid in southwest Japan using strain rates and seismic catalog.
In order to evaluate the seismic potential, we used the GNSS velocity obtained by Kimura et al. (2019) and seismic catalogs by JMA and Utsu (1982, 1985, 2004). For the GNSS velocity, we removed the interplate coupling and rigid motion of each crustal block. Then, we calculated the geodetic seismic moment rate at each grid from the strain rate and the thickness of the seismogenic layer (D90 in this research) using the equation that Savage & Simpson (1997) proposed and Nishimura (2022) revised. On the other hand, we estimated the b-value of the TGR-law and the maximum magnitude at each grid from the seismic catalogs. Then, we calculated the a-value of the TGR-law from the geodetic seismic moment rate, b-value, and the maximum magnitude, assuming that the geodetic seismic moment rate is equal to the total seismic moment rate released by earthquakes. Next, we converted the estimated number of possible earthquakes larger than Mw6.0 using a-value. As a result, we evaluated inland seismic potential larger than Mw6.0 in 30 years, based on the Poisson process.
We estimate the inland seismic potential between around 0.001% and 3%. The area with a higher value was seen in the central Kyushu region and along some tectonic lines. Since the strain rate distribution is quite similar to the estimated seismic potential, the strain rate can significantly influence the seismic potential. In comparison with the epicenter of past major earthquakes, the calculated seismic potential can reflect the inland seismicity. On the other hand, in comparison with Nishimura (2022), the distributions of the strain rate and the inland seismic potential were similar to this research. In addition, we estimated the inland seismic potential with equal to or larger than Mj6.8 to compare with the regional evaluation of active faults by the HERP. While the inland seismic potential in this research fell within the 95% confidence interval of those by the HERP in northern and eastern Chugoku, Shikoku, and southern Kyushu, the former was smaller than the interval of the latter in western Chugoku, and northern and central Kyushu. The cause of this discrepancy can be that the strain rate in this research was not so high as the density of the major active fault zone in the region. However, we need to improve our methods, such as estimating the ratio of the elastic part to the total quantity in the geodetic seismic moment rate or using the past earthquake history and average displacement rate in major active fault zones, which is used in the evaluation by the HERP, in the future.
In order to evaluate the seismic potential, we used the GNSS velocity obtained by Kimura et al. (2019) and seismic catalogs by JMA and Utsu (1982, 1985, 2004). For the GNSS velocity, we removed the interplate coupling and rigid motion of each crustal block. Then, we calculated the geodetic seismic moment rate at each grid from the strain rate and the thickness of the seismogenic layer (D90 in this research) using the equation that Savage & Simpson (1997) proposed and Nishimura (2022) revised. On the other hand, we estimated the b-value of the TGR-law and the maximum magnitude at each grid from the seismic catalogs. Then, we calculated the a-value of the TGR-law from the geodetic seismic moment rate, b-value, and the maximum magnitude, assuming that the geodetic seismic moment rate is equal to the total seismic moment rate released by earthquakes. Next, we converted the estimated number of possible earthquakes larger than Mw6.0 using a-value. As a result, we evaluated inland seismic potential larger than Mw6.0 in 30 years, based on the Poisson process.
We estimate the inland seismic potential between around 0.001% and 3%. The area with a higher value was seen in the central Kyushu region and along some tectonic lines. Since the strain rate distribution is quite similar to the estimated seismic potential, the strain rate can significantly influence the seismic potential. In comparison with the epicenter of past major earthquakes, the calculated seismic potential can reflect the inland seismicity. On the other hand, in comparison with Nishimura (2022), the distributions of the strain rate and the inland seismic potential were similar to this research. In addition, we estimated the inland seismic potential with equal to or larger than Mj6.8 to compare with the regional evaluation of active faults by the HERP. While the inland seismic potential in this research fell within the 95% confidence interval of those by the HERP in northern and eastern Chugoku, Shikoku, and southern Kyushu, the former was smaller than the interval of the latter in western Chugoku, and northern and central Kyushu. The cause of this discrepancy can be that the strain rate in this research was not so high as the density of the major active fault zone in the region. However, we need to improve our methods, such as estimating the ratio of the elastic part to the total quantity in the geodetic seismic moment rate or using the past earthquake history and average displacement rate in major active fault zones, which is used in the evaluation by the HERP, in the future.