09:15 〜 09:30
[SSS10-06] スラブ内とプレート境界における地震発生パターンの異なりと、繰り返し地震誤検出の可能性
キーワード：繰り返し地震、断層サイズ、2003年宮城沖スラブ内地震、波形相関
Repeating earthquakes (REs) provide unique data for detecting aseismic slip through their repeated ruptures of the same fault area. While REs are common at plate boundaries, their occurrence within slabs and crusts has been recently suggested. However, how arbitrary thresholds used in RE detection methods (e.g., waveform correlation or distance thresholds) influence the final results remains poorly understood. Using 13,000 M>2 earthquakes near the 2003 Mw 7.0 Miyagi-oki intraslab earthquake, we examine earthquake repetition in both interplate and intraslab environments in detail.
After relocation, we identified 400 RE pairs based on source overlapping, all occurring on the plate boundary with none within the slab. These REs show shorter rupture durations and higher stress drops than expected from typical 3-10 MPa stress drops, suggesting that RE detection based on typical stress drops and loose criteria may misidentify adjacent earthquakes as REs.
While REs show very high correlation (cc > 0.98), adjacent earthquakes also exhibit high correlation (cc > 0.95), indicating that high waveform correlation alone does not necessarily identify REs at the same location. For adjacent earthquake pairs (~400 m distance), waveform similarity gradually decreases with increasing hypocentral distance, likely due to seismic scattering. This suggests that moderately distant stations, where scattering effects dominate internal attenuation, may be more suitable for RE detection. Intraslab events exhibit systematically lower correlation coefficients than interplate events for given interevent distances, suggesting either greater diversity in focal mechanisms or stronger structural heterogeneity in the slab environment.
The interevent distance distribution reveals a clear contrast: concentrated overlapping for interplate events versus scattered distribution for intraslab events. This difference possibly reflects different contributions of aseismic and seismic slip on faults, varying degrees of patch isolation, and different fault geometries (single plate boundary versus multiple planes in the slab) and maturity. Careful assessment is needed when evaluating repeating earthquakes in environments like the slab interior, where seismicity is not necessarily confined to isolated areas.
After relocation, we identified 400 RE pairs based on source overlapping, all occurring on the plate boundary with none within the slab. These REs show shorter rupture durations and higher stress drops than expected from typical 3-10 MPa stress drops, suggesting that RE detection based on typical stress drops and loose criteria may misidentify adjacent earthquakes as REs.
While REs show very high correlation (cc > 0.98), adjacent earthquakes also exhibit high correlation (cc > 0.95), indicating that high waveform correlation alone does not necessarily identify REs at the same location. For adjacent earthquake pairs (~400 m distance), waveform similarity gradually decreases with increasing hypocentral distance, likely due to seismic scattering. This suggests that moderately distant stations, where scattering effects dominate internal attenuation, may be more suitable for RE detection. Intraslab events exhibit systematically lower correlation coefficients than interplate events for given interevent distances, suggesting either greater diversity in focal mechanisms or stronger structural heterogeneity in the slab environment.
The interevent distance distribution reveals a clear contrast: concentrated overlapping for interplate events versus scattered distribution for intraslab events. This difference possibly reflects different contributions of aseismic and seismic slip on faults, varying degrees of patch isolation, and different fault geometries (single plate boundary versus multiple planes in the slab) and maturity. Careful assessment is needed when evaluating repeating earthquakes in environments like the slab interior, where seismicity is not necessarily confined to isolated areas.