Stress Drop Variation of Deep-Focus Earthquakes Based on Empirical Green's Functions

Abstract

We analyze source characteristics of global, deep-focus (>350 km) earthquakes with moment magnitudes (Mw) larger than 6.0–8.2 using teleseismic P-wave and S-wave spectra and an empirical Green's functions approach. We estimate the corner frequency assuming Brune's source model and calculate stress drops assuming a circular crack model. Based on P-wave and S-wave spectra, the one standard deviation ranges are 3.5–369.8 and 8.2–328.9 MPa, respectively. Based on the P-wave analysis, the median of our stress drop estimates is about a factor of 10 higher than the median stress drop of shallow earthquakes with the same magnitude estimated by Allmann and Shearer (2009, https://doi.org/10.1029/2008JB005821). This suggests that, on average, the shear stress of deep faults in the mantle transition zone is an order of magnitude higher than the shear stress of faults in the crust. The wide range of stress drops implies coexistence of multiple physical mechanisms.