Constraining the source location of the 30 May 2015 (M-w 7.9) Bonin deep-focus earthquake using seismogram envelopes of high-frequency P waveforms: Occurrence of deep-focus earthquake at the bottom of a subducting slab

摘要

In this study, the source location of the 30 May 2015 (M-w 7.9) deep-focus Bonin earthquake was constrained using P wave seismograms recorded across Japan. We focus on propagation characteristics of high-frequency P wave. Deep-focus intraslab earthquakes typically show spindle-shaped seismogram envelopes with peak delays of several seconds and subsequent long-duration coda waves; however, both the main shock and aftershock of the 2015 Bonin event exhibited pulse-like P wave propagations with high apparent velocities (similar to 12.2 km/s). Such P wave propagation features were reproduced by finite-difference method simulations of seismic wave propagation in the case of slab-bottom source. The pulse-like P wave seismogram envelopes observed from the 2015 Bonin earthquake show that its source was located at the bottom of the Pacific slab at a depth of similar to 680 km, rather than within its middle or upper regions.