5:15 PM - 6:30 PM
[SSS07-P07] Deep crustal seismicity in Hiroshima Prefecture
Keywords:crust, seismicity , D90
The thickness of the seismogenic layer and the lateral variation are important parameters for understanding the generation mechanism of crustal seismicity and earthquake hazard analysis [e.g., Iio et al., 2002].
The spatial distribution of D90, which corresponds to the cutoff depth for shallow earthquakes is obtained for the entire Japan by Omuralieva et al. [2012]. They showed that the lateral variation of D90 ranges from about 5 km to 40 km. Some remarkably deep D90 areas are found in the fore-arc side of east Japan along the Pacific coast. In the study, the causes of these locally deep D90 are explained by cooling effect of the subducting oceanic plate. There is another locally deep D90 area found in Hiroshima Prefecture, in the southwest part of the Chugoku region in southwestern Japan. The locally deep D90 in Hiroshima Prefecture is also considered to be caused by the cooling effect of the subducting Philippine Sea plate. Beneath this area, the Philippine Sea plate subducts at a very shallow angle, which may effectively cool the above inland crust [Omuralieva et al., 2012].
In this study, we analyze the characteristics of the locally deep seismicity in Hiroshima Prefecture. The seismicity distributes in the area with radius 10 km, centered at 34.5N, 132.7E. The deepest earthquakes occurred at ~ 30 km depths. The most magnitudes of the earthquakes are smaller than 3.0. We also investigate seismic wave velocities in the source region and the surroundings of the locally deep seismicity. The Vp and Vs are relatively high in the southern part of the seismicity area. This may give additional insight to the cause of the locally deep seismicity.
The spatial distribution of D90, which corresponds to the cutoff depth for shallow earthquakes is obtained for the entire Japan by Omuralieva et al. [2012]. They showed that the lateral variation of D90 ranges from about 5 km to 40 km. Some remarkably deep D90 areas are found in the fore-arc side of east Japan along the Pacific coast. In the study, the causes of these locally deep D90 are explained by cooling effect of the subducting oceanic plate. There is another locally deep D90 area found in Hiroshima Prefecture, in the southwest part of the Chugoku region in southwestern Japan. The locally deep D90 in Hiroshima Prefecture is also considered to be caused by the cooling effect of the subducting Philippine Sea plate. Beneath this area, the Philippine Sea plate subducts at a very shallow angle, which may effectively cool the above inland crust [Omuralieva et al., 2012].
In this study, we analyze the characteristics of the locally deep seismicity in Hiroshima Prefecture. The seismicity distributes in the area with radius 10 km, centered at 34.5N, 132.7E. The deepest earthquakes occurred at ~ 30 km depths. The most magnitudes of the earthquakes are smaller than 3.0. We also investigate seismic wave velocities in the source region and the surroundings of the locally deep seismicity. The Vp and Vs are relatively high in the southern part of the seismicity area. This may give additional insight to the cause of the locally deep seismicity.