Temporal Variations in and Above a Megathrust Following Episodic Slow‐Slip Events

Abstract

AbstractRecent observations beneath central Japan have shown that periodic fluid drainage occurs during slow‐slip events (SSEs) based on temporal variations in above the megathrust boundary of the subducting Philippine Sea slab. However, no previous studies have estimated associated . A comparison of and can provide clues to the mechanism of seismic attenuation because of different propagation characteristics of the two waves. We estimate temporal variations in and via spectral analyses of waveform data from November 2009 to August 2021 period. The results indicate that both and exhibit temporal variations at about 1‐year periodicity and there are systematic differences between and that have smaller values, less insignificant variation, and weaker correlations with SSEs. Furthermore, increases concurrent with SSEs. These differences suggest that attenuation is caused by the wave‐induced fluid flow. could be an important parameter for detecting the presence of fluid.