The Depth-dependent Earthquake Stress Drop and Energy Radiation in Japan Subduction Zone

Abstract:

Widespread and high rate of intermediate earthquakes in the Japan subduction zone open the door to systematically investigating the depth-varying characteristics of earthquake sources. Compared to the magathrust events rupturing on the interface between overriding plate and subducting slab, the depth-varying characteristics of intermediate earthquakes are still poorly understood. The major difficulty in this issue is that the source characteristic is always concealed from the effects along the raypaths. Here, we utilize the cluster-event method to ensure a robust inversion for source and path parameters for 813 events spreading over a depth range of 0 – 150 km and seismic moments 4 orders of magnitude different. Static and dynamic source parameters are measured and compared for three depth regions: I, 0-25 km; II, 25-50 km; and III, > 50 km, where distinct rupture mechanisms may dominate. Our resulting corner frequency, stress drop, and radiated energy provide strong evidence of depth-dependent characterizations of earthquake sources. The estimations of higher corner frequency and stress drop at greater depth with sufficient short-period energy radiation indicate a relatively concentrated earthquake nucleation. The thermal shear instability, dehydration related process or mixed of them may be responsible for these rupture characterizations of earthquakes.