2:30 PM - 2:45 PM
[SCG60-09] Split of the Philippine Sea plate and non-volcanic seismic swarm in Wakayama district, SW Japan
In 2013, we conducted a new seismic experiment (deployment of 40 portable seismic stations) to investigate the structure between Wakayama district and Awaji Island at the western extension of the seismic swarm area, where the Philippine Sea Plate has been proposed to split (Ide et al., 2010). From a new receiver function image with high spatial resolution, we found that the dehydrated oceanic crust (high-velocity without intra-slab seismicity) steeply gets to be shallow toward offshore from Wakayama district and close to the bottom of the overlying crust beneath Awaji Island. Interestingly, we found out a split or gap of the oceanic crust beneath the center of Awaji Island. However, the gap width appears to be significantly smaller than one proposed by Ide et al. (2010). Due to this split of the oceanic crust, hot mantle is easily leaking into the mantle wedge beneath Wakayama district, resulting to warm thermal condition. These anomalous structures of the oceanic crust and mantle wedge may locally promotes dehydration reactions of the subducting oceanic crust, leading to local increase in fluid flux to the shallow seismic swarm area.