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[SSS30-19] Randomness of megathrust earthquakes implied by rapid stress recovery after the 2011 Tohoku-oki earthquake
Keywords:Tohoku-oki earthquake, earthquake cycle, seismicity, b-value, differential stress
Our analysis reveals that the spatial distribution of b-values reflects well the tectonic processes accompanying plate motion. However, there is no evidence of distinct earthquake-generation regions along the megathrust, associated with the so-called "characteristic earthquakes".
Nevertheless, we show that parts of the plate interface that ruptured during the 2011 Tohoku-oki earthquake were highly stressed in the years leading up to the earthquake, as expressed by mapped, very low regional b-values. Although the stress was largely released during the 2011 rupture, thus leading to an increase in b-values immediately after the megathrust event, the stress levels (i.e., b-values) quickly recovered to pre-megaquake levels within just a few years. This suggests that the megathrust zone is likely ready for large earthquakes any time with a low but on average constant probability.
Our results imply that large earthquakes may not have a characteristic location, size or recurrence interval, and might therefore occur more randomly distributed in time. The findings also bring strong evidence that the size distribution of earthquakes is sensitive to stress variations and its careful monitoring can improve the seismic hazard assessment of the megathrust zone.
Thessa Tormann, Bogdan Enescu, Jochen Woessner, Stefan Wiemer, Randomness of megathrust earthquakes implied by rapid stress recovery after the Japan earthquake, Nature Geoscience, 8, 152-158, doi:10.1038/ngeo2343, 2015.