2:45 PM - 3:00 PM
[SSS16-05] Seismic reflector above the non-volcanic tremor along the Philippine Sea Plate
Keywords:plate boundary, reflector, non-volcanic tremor
It is remarkable characteristic of the seismic experiments in this region that the clear reflected wave around the plate boundary was detected. The clear reflected wave was explained as a reflected wave at the top of the extremely low-velocity layer, which was located at the top of the subducting Philippine Sea slab (e.g, Kodaira et al., 2002; Iidaka et al., 2004). The P-wave velocity values of the thin layer were 3 km/s and 2 km/s in the Nankai and Tokai regions, respectively (Kodaira et al., 2002; Iidaka et al 2004). Similar strong reflector was also detected at the eastern part of the Kii Peninsula (Iwasaki et al., 2016). The locations of the strong reflectors are compared with the source area of the non-volcanic tremor. In the Nankai region, the depth of the reflector was located at 10 km – 30 km (Kodaira et al., 2002). The source area of the tremor is located at the deepest part of the low velocity layer. In the Tokai region, the extremely low velocity layer is located just above the source area of the tremor. Iwasaki et al. (2016) also reported that the strong reflector was located just above the source area of the tremor in the eastern part of the Kii peninsula. At the three areas, the strong reflector was located above the source area of tremor. The seismic structure of the S-wave structure at the tremor area was characterized to be high-velocity mantle wedge and low-velocity oceanic crust (Igarashi and Iidaka, 2017). It is expected that the low velocity layer seems to be related to the dehydration of the oceanic crust.
The non-volcanic tremor had been reported at many subduction zones. Song et al. (2009) reported the ultra low velocity layer in the Mexico subduction zone. The ultra low velocity layer is located at top of the slab. The low velocity layer is located in shallower than tremor area. The extremely low-velocity layer has been reported at several subduction zones. The research of the characteristics of the low-velocity layer is very important to know the source of the non-volcanic tremor.