** Progress in Earth and Planetary Science is the official journal of the Japan Geoscience Union, published in collaboration with its society members.
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Solid earth sciences
202306202306
Aftershocks following the 2011 Tohoku-Oki earthquake driven by both stress transfer and afterslip
Taku Ueda, Aitaro Kato
Aftershock, Stress transfer, Afterslip, 2011 Tohoku-Oki earthquake, HIST-ETAS model, Background earthquakes, Triggered earthquakes
(Up) Interpretation of the aftershock generation mechanisms following the 2011 Tohoku-Oki earthquake. The red line denotes the plate interface (Nakajima and Hasegawa 2006; Kita et al. 2010), and the gray circles are the hypocenters of the events in the F-net hypocenter catalog (11/03/2011-11/03/2021).
(Down) Temporal variations in the number of background earthquakes downdip of the large coseismic slip zone compared with the aseismic slip amount and the afterslip.
Aftershocks are a fundamental characteristic of seismicity, and their generation mechanism is mainly characterized by two physical models, stress transfer from large earthquakes and afterslip-induced stress loading. However, the contribution of each mechanism to aftershock generation remains unclear. Here we investigate the spatiotemporal variations in aftershock activity following the 2011 Tohoku-Oki earthquake by applying the Hierarchical Space–Time Epidemic-Type Aftershock Sequence (HIST-ETAS) model to the decade of recorded seismicity since the mainshock. Using the estimated HIST-ETAS model, we categorize the aftershocks into background earthquakes (which are caused by aseismic phenomena) and triggered earthquakes (which are caused by earthquake-to-earthquake interactions). Most of the earthquakes that occurred updip of the large coseismic slip zone along the Japan Trench are triggered earthquakes, consistent with the lack of afterslip in this area. Conversely, background earthquakes are the predominant earthquake type in the long-term downdip of the large coseismic slip zone, and they positively correlate with the afterslip evolution. Our results suggest the importance of combining these two end-member aftershock generation models to explain aftershock activity and thus provide new insights into the relationship between afterslip and spatiotemporal aftershock distribution. Our classifications may also contribute to the monitoring of afterslip in a given region that hosts a large earthquake, particularly where geodetic observation networks are too sparse to evaluate afterslip evolution.
