Time-Dependent Seismic Hazard Above the South America Subduction Zone in Central and Southern Chile

Abstract eng:
The Peru-Chile portion of the South America subduction zone is one of the most seismically active regions in the world and the source of some of the largest known earthquakes, including the 1960 moment magnitude (M) 9.5 Great Chile earthquake and more recently, the 2010 M 8.8 Maule earthquake. Since the beginning of the historical record in the mid1500s, there have been at least 10 earthquakes of M 8 and larger principally due to rupture of the megathrust based on reported tsunamis. We have performed probabilistic seismic hazard analyses (PSHA) for four cities above the subduction zone in central and southern Chile. We have included a time-dependent model for the region's most significant seismic source, the two southernmost segments of the South America subduction zone megathrust: the Concepcion-Valparaiso and Southern Chile segments. Our time-dependent model is based principally on the historical record and the challenge was to characterize the significant uncertainties in the segmentation, recurrence, and maximum magnitudes of the megathrust earthquakes that have occurred and will occur along the subduction zone. The PSHA seismic source model also includes crustal faults, crustal background seismicity, and the Wadati-Benioff zone. A number of crustal faults are located above the South America megathrust although it is unclear whether these are independent seismic sources or rupture coseismically with the megathrust. An additional critical issue that needs to be addressed in the PSHA is the selection of ground motion prediction models. We used the Next Generation of Attenuation (NGA)-West2 models for the crustal seismic sources and recent global models for both the megathrust and the Wadati-Benioff zone. We also compared these latter models with the strong motion data from the 2010 Maule earthquake. Assuming generic soil site conditions, we computed the hazard for the cities of Valparaiso, Concepcion, Temuco, and Puerto Montt. We compare our probabilistic hazard results with a time-independent model of the two southern segments of the South America megathrust to evaluate the impact of the time-dependent model on the hazard in central and southern Chile.

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