[SCG48-P26] Underground structure around source region of slow earthquakes in western Shikoku obtained by receiver function analysis
Keywords:Receiver function, episodic tremor and slip, long-term slow slip event, low seismic velocity layer
As a result, continuous continental Moho and oceanic crust are clearly imaged along both north-south and east-west oriented seismic lines. The plate boundary in the south part, where the distinct continental Moho is not imaged, has steeper slope than the north part along the north-south line. ETS occurs between the mantle wedge and the subducting plate, and long-term SSE occurs along a contact between the continental crust and the oceanic crust.
We show that the oceanic crust indicates much higher Vp/Vs than the hanging wall by using also the reverberation phases. This high Vp/Vs means the elevated fluid pore pressure within oceanic crust due to dehydration. Vp/Vs in the oceanic crust is higher in the deep part of the long-term SSE region than in the ETS region like as the case of Tokai. It is assumed that fluid would accumulate within the oceanic crust owing to low permeability of the continental crust in the long-term SSE region. In contrast, serpentinization of the mantle wedge just above the ETS region could reduce fluid pressure in the oceanic crust. Furthermore, Vp/Vs in the oceanic crust becomes lower in the deeper part beyond the ETS depths, suggesting that eclogization is completed at the depths.