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Variability of ETAS Parameters in Global Subduction Zones and Applications to Mainshock–Aftershock Hazard Assessment

Lizhong Zhang, Maximilian J. Werner, & Katsuichiro Goda

Published January 14, 2020, 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 giant
shock, we assess the variability of the epidemic-type aftershock sequence (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, given individual sequences have fewer data including missing early
aftershocks. 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 from robust estimates
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 M 8.0–9.0 events are included in a region, mainly because an M 9.0 sequence
dominates the number of events in the catalog. Based on the ETAS parameter estimates
in the long time period window, we propose a set of ETAS parameters for future M 9.0
sequences for aftershock hazard assessment (K0  0:04 0:02, α  2:3, c  0:03 0:01,
p  1:21 0:08, γ  1:61 0:29, d  23:48 18:17, and q  1:68 0:55). Synthetic catalogs
created with the suggested ETAS parameters show good agreement with three observed
M 9.0 sequences since 1965 (the 2004 M 9.1 Aceh–Andaman earthquake, the 2010 M 8.8
Maule earthquake, and the 2011 M 9.0 Tohoku earthquake).

Zhang, L., Werner, M. J., & Goda, K. (2020). Variability of ETAS Parameters in Global Subduction Zones and Applications to Mainshock–Aftershock Hazard Assessment. Bulletin of the Seismological Society of America, 110(1), 191-212. doi: 10.1785/0120190121.

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