Earthquake Depth Phase Extraction With P Wave Autocorrelation Provides Insight Into Mechanisms of Intermediate-Depth Earthquakes

Constraining the mechanism of earthquakes in subduction zones requires adequate estimates of source location and near-source elastic properties. In this study, we propose a P wave autocorrelation-based method to extract depth phase energy from teleseismic earthquakes with moment magnitude down to 4.0. We apply the method to improve location estimates of intermediate-depth earthquakes in the Japan and northern Chile subduction zones, which represent so-called cold and warm slabs, respectively, and which are both marked by double seismic zones. A positive correlation of slab age and double-seismic-zone width validates a thermally controlled model of slab morphology. The negative to normal differential times (and, thus, low or normal Vp/Vs) of the deep parts of the double seismic zones suggest that the intermediate-depth earthquakes considered here are not due to dehydration.