Slab interactions in the Taiwan region based on the P- and S-velocity distributions in the upper mantle

• P- and S-velocity anomalies in the mantle beneath Taiwan are presented.
• Seismic tomography clearly reveals two slabs beneath Taiwan.
• The origin of Taiwan is due to collision of two oppositely oriented subduction zones.

We present a new model of P- and S-velocity anomalies in the upper mantle beneath the Taiwan region based on the inversion of travel time data from the global International Seismological Center (ISC) catalog. We clearly observed the anomalies of high P- and S-velocities associated with the subducting plates beneath the Ryukyu and Luzon arcs. At depths in the range of 100–200 km, the anomalies related to both slabs seem to be connected, which might be evidence of the lithosphere collision of the two oppositely oriented subduction zones. This model has been carefully verified using different synthetic tests. Based on the derived seismic model, we propose a model of recent plate reconstructions in the region around Taiwan. Initially, we presume the existence of two oppositely oriented subduction zones underneath the Luzon Island and the Ryukyu arc, separated with a transform fault. The NW movement of the Philippine Sea Plate led to first a shortening and then a disappearance of this transform fault. As a result, the edge of the Luzon arc collided with the edge of the Ryukyu arc. Simple simulations indicate that in this edge area, very strong stresses and deformation might take place that result in significant shortening of the earth surface. We believe that the origin of the Taiwan island was caused by the collisional processes due to the interaction of the two subduction zones. Note that in this case, no other conditions, such as the existence of arcs and/or buoyant continental crustal blocks, are required to explain the origin of the thick, strongly shortened crust in Taiwan.