Seismic imaging of southwest Japan using P and PmP data: Implications for arc magmatism and seismotectonics

To better understand the relationship between crustal heterogeneity and seismotectonics and arc magmatism, we determined a detailed P-wave velocity structure of the crust under a north–south belt area in Southwest Japan by using the first arriving P-waves and the reflected P-waves from the Moho discontinuity (PmP) from 60 crustal earthquakes recorded by 29 seismic stations. Our results revealed significant low-velocity anomalies beneath the fault zone of the Median Tectonic Line and the Daisen volcano, which suggest that Daisen is potentially an active volcano. In the lower crust, we detected low-velocity anomalies overlying the subducting Philippine Sea plate, which may indicate the existence of fluids released by the slab dehydration. The 1955 southern Tokusima earthquake (M 6.4) occurred between low and high high-velocity zones. The 2000 western Tottori earthquake (M 7.3) and other nearby strong earthquakes occurred around the Daisen volcano, which may be related to the upwelling magma and fluids.