11:00 〜 13:00
[SCG44-P26] Temporal and spatial variations in seismicity characteristics after the 2011 Tohoku-Oki earthquake estimated from HIST-ETAS model
Epidemic Type Aftershock Sequence (ETAS) model (e.g., Ogata, 1988, 1998) represents seismicity rate as a summation of background seismicity rate, which is caused by tectonic loading or aseismic phenomena, and rate of aftershock which is caused by earthquake-to-earthquake interaction. The Hierarchical Space-Time ETAS (HIST-ETAS) model (e.g., Ogata, 2004) represents the parameters as a function of space. Therefore, we can discuss the spatial variations in seismicity characteristics using this model. In addition, we can discuss the temporal variations in background seismicity and aftershocks by calculating the summation of the probability that each event is a background event or an aftershock using the estimated HIST-ETAS model.
The 2011 M9 Tohoku-Oki earthquake occurred on March 11, 2011 along the boundary between the subducting Pacific Plate and the overriding plate. Previous studies reveal that the activation and quiescence of seismicity in and around focal area of this megathrust earthquake (e.g., Asano et al., 2011; Kato and Igarashi, 2012). In this study, we applied the HIST-ETAS model to the seismicity > M4 after the 2011 Tohoku-Oki earthquake to overview the decadal evolution of the aftershocks. We consider the physical processes of seismicity activation around the focal area of this megathrust earthquake based on temporal and spatial variations in background events and aftershocks.
Along the Japan Trench in the up-dip of the large coseismic slip zone, aftershocks are predominant in the long-term with very few background events, suggesting that seismicity activation is caused by earthquake-to-earthquake interaction. In the down-dip of the large coseismic slip zone, the background seismicity contributes to long-term seismicity activation, decreases with time (1/t) and positively correlates with the amount of aseismic slip calculated using similar earthquake catalog (Igarashi, 2020) and afterslip estimated by geodetic inversion (Fukuda and Johnson, 2021). This result suggests that seismicity activation is caused by the afterslip driven by the 2011 Tohoku-Oki earthquake.
Acknowledgements: The JMA catalog was used; the code of Ogata et al. (2021) was used to estimate parameters of the HIST-ETAS model. The similar earthquake catalog (Igarashi, 2020) was used. We thank J. Fukuda for providing afterslip data of the 2011 Tohoku-Oki earthquake (Fukuda and Johnson, 2021).
The 2011 M9 Tohoku-Oki earthquake occurred on March 11, 2011 along the boundary between the subducting Pacific Plate and the overriding plate. Previous studies reveal that the activation and quiescence of seismicity in and around focal area of this megathrust earthquake (e.g., Asano et al., 2011; Kato and Igarashi, 2012). In this study, we applied the HIST-ETAS model to the seismicity > M4 after the 2011 Tohoku-Oki earthquake to overview the decadal evolution of the aftershocks. We consider the physical processes of seismicity activation around the focal area of this megathrust earthquake based on temporal and spatial variations in background events and aftershocks.
Along the Japan Trench in the up-dip of the large coseismic slip zone, aftershocks are predominant in the long-term with very few background events, suggesting that seismicity activation is caused by earthquake-to-earthquake interaction. In the down-dip of the large coseismic slip zone, the background seismicity contributes to long-term seismicity activation, decreases with time (1/t) and positively correlates with the amount of aseismic slip calculated using similar earthquake catalog (Igarashi, 2020) and afterslip estimated by geodetic inversion (Fukuda and Johnson, 2021). This result suggests that seismicity activation is caused by the afterslip driven by the 2011 Tohoku-Oki earthquake.
Acknowledgements: The JMA catalog was used; the code of Ogata et al. (2021) was used to estimate parameters of the HIST-ETAS model. The similar earthquake catalog (Igarashi, 2020) was used. We thank J. Fukuda for providing afterslip data of the 2011 Tohoku-Oki earthquake (Fukuda and Johnson, 2021).