Subsurface structures derived from receiver function analysis and relation to hypocenter distributions in the region from the eastern Shikoku to the northern Chugoku districts, Southwest Japan

摘要

We carried out receiver function imaging to estimate detailed configurations of the Philippine Sea (PHS) slab beneath the Shikoku and Chugoku districts and crustal structures in the region. We used two temporary seismic arrays with an average station spacing of about 10 km in the Chugoku district. Beneath Shikoku a clear northward dipping discontinuity at about 20-40 km depth was found, with other discontinuities below. We present a new interpretation that the clear boundary corresponds to the under surface of a low velocity layer in the upper part of the PHS slab. We also found a discontinuity at about 60 km depth beneath the Chugoku district, which is thought to be the aseismic PHS slab. Small scale discontinuities were found in the crust beneath the source area of the 2000 western Tottori Earthquake and around the Median Tectonic Line. The discontinuities might relate to the occurrence of large inland earthquakes.