09:45 〜 10:00
[SIT20-04] Diverse-source parameters of deep earthquakes
キーワード：深発地震
The mechanism of deep earthquakes in subducting slabs remains enigmatic. We analyze five groups of similar earthquakes (depth > 200 km) in the Pacific Plate beneath central Japan, whose waveforms are similar at five or more stations over a 40 s time window that includes the P and S arrivals. Hypocenter relocations using waveform-derived differential-time data suggest that similar-deep earthquakes occur on complementary ruptures of neighboring patches on a fault, rather than by repeatedly rupturing the same fault patch. The stress drops of similar earthquakes are almost constant within each group but differ by an order of magnitude even between groups separated by ~20 km, while the scaled energy and radiation efficiency are significantly different even for each group. The wide range of source parameters estimated for similar earthquakes in a common slab environment suggests that the source parameters can be significantly affected by small-scale heterogeneities along the fault. This characteristic is also applicable for the other deep earthquakes at the same depths as the similar earthquakes we analyze. Thus, the predominant-rupture process of deep earthquakes can be different even on the same fault plane or at identical depths in a common slab. A dual-process that includes both seismic ruptures assisted by fluid-related embrittlement and thermal shear instability might have a possibility to explain the generation mechanism of deep earthquakes.