Topography of the Seismic Velocity Discontinuities beneath the Chugoku and Shikoku Districts,Southwest Japan |
| |
| Authors: | Email author" target="_blank">Hitoshi?OdaEmail author Michiro?Okamoto Motoko?Ishise |
| |
| Institution: | (1) Department of Earth Sciences, Okayama University, Okayama 700-8530, Japan |
| |
| Abstract: | The first P-arrival-time data from 513 local earthquakes were analyzed to study lateral variation of the depth to the Conrad
and Moho discontinuities beneath the Chugoku and Shikoku districts, southwest Japan, as well as to determine earthquake hypocenters
and P-wave station corrections. The depth to the discontinuity was estimated by minimizing the travel-time residuals of more
than 8700 first P arrivals observed at 55 seismic stations. The Conrad and Moho discontinuities are located within depth ranges
of 15–25 km and 30–40 km, respectively. The Moho is deeper under the mountain area than under the Seto Inland Sea area, and
especially deep under the Pacific Coast of the Shikoku district and the mountain area in the Chugoku district. The depth variation
of the Moho is quite similar to the Bouguer gravity anomaly distribution and the lateral variations of the P-wave velocity.
The deep Moho under the southern Shikoku is located at the portion in which the continental Moho under the island arc meets
the oceanic Moho that is the boundary interface between the oceanic crust and the Philippine Sea (PHS) plate dipping toward
the back arc. Although there are high mountains in the northern and middle Shikoku, the Moho is not so deep because subduction
of the PHS plate prevents the Moho from getting deep, while the Moho is deep due to isostatic balance under the mountain area
in the Chugoku district. In addition, we indicated the possibility that the upper boundary of the oceanic crust just above
the high-velocity PHS plate is in contact with the deep Moho under the western Chugoku. The contact of the Moho with the oceanic
crust can explain the markedly negative gravity anomaly observed in the western Chugoku and the later phase that appears just
after the first P arrival from local earthquakes. |
| |
| Keywords: | Conrad and Moho discontinuities Seismic tomography Gravity anomaly Philippine Sea plate Chugoku and Shikoku districts Southwest Japan |
| 本文献已被 SpringerLink 等数据库收录！ |
|
