5:15 PM - 6:45 PM
[SSS10-P11] Impact of Changing the Earthquake Number Ratio (Interplate/Intraplate) Model on Seismic Hazard Assessment
Keywords:Interplate earthquakes, Intraplate earthquakes, Seismic hazard assessmentazard assessment, Uncertainty
Subduction earthquakes are classified into interplate earthquakes, which occur on the upper surface of a subducting oceanic plate and intraplate earthquakes, which occur within a subducting plate. Observed seismic intensities during the intraplate earthquakes are greater than interplate earthquakes of the same magnitude and distance. It is therefore necessary to model and evaluate them separately for strong-motion prediction or seismic hazard assessment.
The number of earthquakes classified by the Earthquake Research Committee (ERC) of Japan has as crustal, interplate, or intraplate earthquakes has increased due to the improvement in the accuracy of estimating the hypocenter location and fault mechanism solutions as a result of the development of the basic seismic observation network. In this study, we modeled the number ratio of interplate/intraplate earthquakes for background earthquakes in advance based on the evaluations by the ERC, and investigated the impact on the seismic hazard assessment. The earthquake number ratios were modeled for each region classified in the probabilistic National Seismic Hazard Maps for Japan, by the ERC.
For earthquakes on the Pacific Plate, the proportion of intraplate earthquakes was larger than the current model in all regions, and the difference was more pronounced in the southern part off the coast of Iwate Prefecture and off the coast of Miyagi Prefecture. The seismic hazard assessment using the ground motion model by Morikawa and Fujiwara (2013) showed that the short-period component (0.1-0.5 s) on the Pacific coast north of the northern Kanto region has a larger hazard than the current model, and the hazard is significantly larger in Sendai near the offshore Miyagi Prefecture.
For earthquakes on the Philippine Sea plate, the number of intraplate earthquakes is larger than that of interplate earthquakes in the current model for the southern Kanto region, based on the results of previous studies of M7-class earthquakes occurring there. However, the number of interplate earthquakes is larger than that of intraplate earthquakes in the new model based on recent earthquakes evaluated by the ERC. However, all recent earthquakes evaluated by the ERC are M5 class or smaller. This means that there is a large uncertainty in the number ratio of interplate/intraplate earthquakes for M7 class, which has a large impact on seismic hazard assessment. The results of the seismic hazard assessment for the Kanto region based on the new model in southern Kanto show no significant difference in the short-period component, but the long-period component with a period of about 1 second is larger than that of the current model. This is due to the fact that the maximum magnitude (M7.8) of an interplate earthquake is much larger than that of an intraplate earthquake (M7.3).
The number of earthquakes classified by the Earthquake Research Committee (ERC) of Japan has as crustal, interplate, or intraplate earthquakes has increased due to the improvement in the accuracy of estimating the hypocenter location and fault mechanism solutions as a result of the development of the basic seismic observation network. In this study, we modeled the number ratio of interplate/intraplate earthquakes for background earthquakes in advance based on the evaluations by the ERC, and investigated the impact on the seismic hazard assessment. The earthquake number ratios were modeled for each region classified in the probabilistic National Seismic Hazard Maps for Japan, by the ERC.
For earthquakes on the Pacific Plate, the proportion of intraplate earthquakes was larger than the current model in all regions, and the difference was more pronounced in the southern part off the coast of Iwate Prefecture and off the coast of Miyagi Prefecture. The seismic hazard assessment using the ground motion model by Morikawa and Fujiwara (2013) showed that the short-period component (0.1-0.5 s) on the Pacific coast north of the northern Kanto region has a larger hazard than the current model, and the hazard is significantly larger in Sendai near the offshore Miyagi Prefecture.
For earthquakes on the Philippine Sea plate, the number of intraplate earthquakes is larger than that of interplate earthquakes in the current model for the southern Kanto region, based on the results of previous studies of M7-class earthquakes occurring there. However, the number of interplate earthquakes is larger than that of intraplate earthquakes in the new model based on recent earthquakes evaluated by the ERC. However, all recent earthquakes evaluated by the ERC are M5 class or smaller. This means that there is a large uncertainty in the number ratio of interplate/intraplate earthquakes for M7 class, which has a large impact on seismic hazard assessment. The results of the seismic hazard assessment for the Kanto region based on the new model in southern Kanto show no significant difference in the short-period component, but the long-period component with a period of about 1 second is larger than that of the current model. This is due to the fact that the maximum magnitude (M7.8) of an interplate earthquake is much larger than that of an intraplate earthquake (M7.3).