Charactering the Eurasian lithosphere at the western end of the Ryukyu subduction

The Ryukyu subduction zone system stretches from Japan to Taiwan, where it ends against the Asian continent. At the surface, the Okinawa trough as a back-arc basin tapers towards NE Taiwan creating an extensional structure there. At depths, the hot, highly convective mantle wedge juxtaposes against the Eurasian lithosphere. The geometry of the boundary between the Eurasian lithosphere and the mantle wedge is unknown. We examined the waveforms for events in the western edge of the subduction zone received by the stations in northern Taiwan. The result showed that the S coda energy is small at stations near Sandiaojiao but significant and complex at other stations. We hypothesize that the S waves to the coastal stations travel mostly within the mantle wedge while those to the more inland stations travel longer paths in the Eurasian lithosphere. The significant coda energy may result from scattering at the heterogeneities in the continental lithosphere. Our main concern is to depict the Eurasia-wedge boundary, which is a critical parameter in understanding the dynamics in the southwestern edge of the Ryukyu subduction system, and to understand the contribution of the heterogeneities in the Eurasian lithosphere.