15:00 〜 16:00
[J08-P-13] Crustal velocity structure and configuration of the subducting Philippine Sea plate beneath the Japanese Islands identified from receiver function analysis
We apply receiver function analyses to estimate the velocity structure in the crust and uppermost mantle and configuration of the subducting Philippine Sea plate beneath the Japanese Islands. The velocity structures beneath each seismic station searched a best-correlated model between an observed receiver function and synthetic one by using a grid search method. We further constructed many vertical cross-sections of the estimated velocity structure models and the depth-converted receiver function images to estimate seismic velocity discontinuities. Repeating earthquake data which occurred in the subducting plate boundary were also used to estimate plate geometries.
The configuration of Philippine Sea plate dips toward the northwest beneath the Japanese Islands. The direction coincides with plate motion. The thickness of the Philippine Sea plate gradually decreases to the northeast after the contact with the underlying Pacific plate beneath the Tokyo metropolitan area. The northeastern margin of the Philippine Sea plate can identify from the decreasing plate thickness. In the subducting plate boundary contacted with the island arc Moho, we identify non-volcanic tremors in the southwestern Japan region and normal earthquakes including small repeating earthquakes in the Ryukyu Islands. The former areas are characterized by high-velocity mantle wedge and low-velocity oceanic crust, whereas relatively low-velocity mantle wedge characterizes the latter areas. Source regions of past inter-plate destructive earthquakes seem to correspond to the high-velocity area in the Philippine Sea slab. These observations may indicate the relationship between slip characteristic of the plate interface and serpentinized materials which reflect dehydration of the subducting oceanic crust.
The configuration of Philippine Sea plate dips toward the northwest beneath the Japanese Islands. The direction coincides with plate motion. The thickness of the Philippine Sea plate gradually decreases to the northeast after the contact with the underlying Pacific plate beneath the Tokyo metropolitan area. The northeastern margin of the Philippine Sea plate can identify from the decreasing plate thickness. In the subducting plate boundary contacted with the island arc Moho, we identify non-volcanic tremors in the southwestern Japan region and normal earthquakes including small repeating earthquakes in the Ryukyu Islands. The former areas are characterized by high-velocity mantle wedge and low-velocity oceanic crust, whereas relatively low-velocity mantle wedge characterizes the latter areas. Source regions of past inter-plate destructive earthquakes seem to correspond to the high-velocity area in the Philippine Sea slab. These observations may indicate the relationship between slip characteristic of the plate interface and serpentinized materials which reflect dehydration of the subducting oceanic crust.