SPdKS analysis of ultra-low velocity zones beneath the Western Pacific

We collected a new data set of 1354 broadband SPdKS waveforms sampling the western Pacific Ocean region. These data indicate that multiple ultra-low velocity zones (ULVZs) exist in this region. We compared these data to synthetic seismograms computed with the axisymmetric finite difference method PSVaxi for a suite of 517 unique ULVZ models. The region beneath the North and South Philippine Sea shows no evidence for ULVZ presence. The region beneath the Coral Sea shows a large ULVZ, which is approximately 700 x 700 km in lateral dimensions and up to 20 km thick. Multiple small scale ULVZs approximately 180 x 180 km and up to 10 km thick are inferred beneath the South China Sea. Our findings are consistent with previous efforts utilizing the ScP seismic phase and provide additional constraints on ULVZ elastic parameters.