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Megathrust earthquakes release and transfer stress that has accumulated over hundreds of years, leading to large aftershocks that can be highly destructive. Understanding the spatiotemporal pattern of megathrust aftershocks is key to mitigating the seismic hazard. However, conflicting observations show aftershocks concentrated either along the rupture surface itself, along its periphery or well beyond it, and they can persist for a few years to decades. Here we present aftershock data following the four largest megathrust earthquakes since 1960, focusing on the change in seismicity rate following the best-recorded 2011 Tohoku earthquake, which shows an initially high aftershock rate on the rupture surface that quickly shuts down, while a zone up to ten times larger forms a ring of enhanced seismicity around it. We find that the aftershock pattern of Tohoku and the three other megathrusts can be explained by rate and state Coulomb stress transfer. We suggest that the shutdown in seismicity in the rupture zone may persist for centuries, leaving seismicity gaps that can be used to identify prehistoric megathrust events. In contrast, the seismicity of the surrounding area decays over 4-6 decades, increasing the seismic hazard after a megathrust earthquake.
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Spatiotemporal Variations of Intermediate‐Depth Earthquakes Before and After 2011 Tohoku Earthquake Revealed by a Template Matching Catalog
Abstract We investigate spatiotemporal changes of intermediate‐depth earthquakes in the double seismic zone beneath Central and Northeastern Japan before and after the 2011 magnitude 9 Tohoku earthquake. We build a template‐matching catalog 1 year before and 1 year after the Tohoku earthquake using Hi‐net recordings. The new catalog has a six‐fold increase in earthquakes compared to the Japan Meteorological Agency catalog. Our results show no significant change in the intermediate‐depth earthquake rate prior to the Tohoku earthquake, but a clear increase in both planes following the Tohoku earthquake. The regions with increased intermediate‐depth earthquake activity and the post‐seismic slips following the Tohoku earthquake are spatially separate and complementary with each other. Aftershock productivity of intermediate‐depth earthquakes increased in both planes following the Tohoku earthquake. Overall, aftershock productivity of the upper plane is higher than the lower plane, likely indicating that stress environments and physical mechanisms of intermediate‐depth earthquakes in the two planes are distinct.
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- PAR ID:
- 10476055
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 50
- Issue:
- 22
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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