Stability of ETAS parameters in global subduction zones and applications to mainshock-aftershock hazard assessment

Lizhong Zhang, Maximilian J. Werner, & Katsuichiro Goda

Submitted May 12, 2019, SCEC Contribution #9081

Megathrust earthquake sequences can impact buildings and infrastructure due to not only the mainshock but also the triggered aftershocks along the subduction interface and in the overriding crust. To give realistic ranges of aftershock simulations in regions with limited data and to provide time-dependent seismic hazard information right after a future M9.0 mainshock, we assess the stability of the ETAS model parameters in subduction zones that have experienced M≥7.5 earthquakes, comparing estimates from long time windows with those from individual sequences. Our results show that the ETAS parameters are more robust if estimated from a long catalog than from individual sequences, due to fewer data, including missing early aftershocks in the individual sequences. Considering known biases of the parameters (due to model formulation, the isotropic spatial aftershock distribution, and finite size effects of catalogs), we conclude that the variability of the ETAS parameters that we observe is not significant, neither across different subduction zone regions nor as a function of maximum observed magnitudes. We also find that ETAS parameters do not change when multiple M8.0-M9.0 events are included in a region, mainly because the M9.0 sequence dominates the number of events in the catalog. Based on the ETAS parameter estimates in the long-time window, we propose one set of ETAS parameters for future M9.0 sequences for aftershock hazard assessment. Synthetic catalogs created with the suggested ETAS parameters show good agreement with three observed M9.0 sequences since 1965 (the 2004 M9.1 Aceh-Andaman earthquake, the 2010 M8.8 Maule earthquake, and the 2011 M9.0 Tohoku earthquake).

Citation
Zhang, L., Werner, M. J., & Goda, K. (2019). Stability of ETAS parameters in global subduction zones and applications to mainshock-aftershock hazard assessment. Bulletin of the Seismological Society of America, (submitted).


Related Projects & Working Groups
Earthquake Forecasting and Predictability, Collaboratory for the Study of Earthquake Predictability