P-wave seismic tomography of the Manila subduction zone

The P-wave velocity perturbation images beneath the Manila Subduction zone are generated by utilizing P-wave arrival times from International Seismological Centre (1960-2008) and the seismic tomographic inversion method. The data set is comprised by 12582 high-quality P-wave arrival times from 1372 regional earthquakes and 14799 travel-time residuals from 2129 teleseismic events. The results show that the shape of the subducted South China Sea slab (SCSs) represented by high velocity anomalies changes with latitudes. From 14 degrees N to 16 degrees N, the subduction angle and depth are both larger than that at 17 degrees N, whereas the SCSs is subducted to the mantle transition zone at a nearly vertical angle at 18 degrees N. The different subduction angles from 17 degrees N to 18 degrees N suggest the slab tearing in the SCSs which turns from nearly-vertical above 300 km depth to horizontal at 200 similar to 300 km depth at 14 degrees N, much different from the distribution of seismic sources, also suggesting the possible slab tearing in the SCSs and the elevation of the 410 km discontinuity. The subduction length and time of SCSs calculated by the tomographic results at different latitudes suggest that the area of the original SCSs was about twice that its present range, and the subduction of the SCSs started at 14 degrees N and propagated from south to north.