10:15 AM - 10:30 AM
[SCG54-06] Temporal and spatial variations in background seismicity 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 and rate of aftershock. 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, the removal of the contribution of aftershock using the HIST-ETAS model provides us the evolution in background seismicity rate.
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 estimated the spatial variations in background seismicity rate μ, the parameters of the Omori-Utsu law (K, p), and the other parameters. Using the estimated parameters, we calculated the probability that each earthquake occurred as background seismicity and investigated the spatial and temporal changes in the background seismicity rate.
Immediately after the 2011 Tohoku-Oki earthquake, the background seismicity rate was higher around the large-slip zone of the 2011 Tohoku-Oki earthquake, which is consistent with the rapid increase in inter-plate earthquakes (Asano et al., 2011; Kato and Igarashi, 2012). The spatial variation in aftershock productivity K is strongly heterogeneous compared with the other parameters (α, p, q). As for temporal variation, the background seismicity has decreased with time (1/t). This result is consistent with the spatial and temporal changes of repeating earthquakes detected by Igarashi (2020) and may reflect aseismic slip associated with the afterslip driven by the Tohoku-Oki earthquake.
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 estimated the spatial variations in background seismicity rate μ, the parameters of the Omori-Utsu law (K, p), and the other parameters. Using the estimated parameters, we calculated the probability that each earthquake occurred as background seismicity and investigated the spatial and temporal changes in the background seismicity rate.
Immediately after the 2011 Tohoku-Oki earthquake, the background seismicity rate was higher around the large-slip zone of the 2011 Tohoku-Oki earthquake, which is consistent with the rapid increase in inter-plate earthquakes (Asano et al., 2011; Kato and Igarashi, 2012). The spatial variation in aftershock productivity K is strongly heterogeneous compared with the other parameters (α, p, q). As for temporal variation, the background seismicity has decreased with time (1/t). This result is consistent with the spatial and temporal changes of repeating earthquakes detected by Igarashi (2020) and may reflect aseismic slip associated with the afterslip driven by the Tohoku-Oki earthquake.