Non-uniform rupture patterns of megathrust earthquakes scenarios: an upgrading of tsunami hazard assessment in Mejillones, northern Chile

Abstract:

Plausible worst-case tsunamigenic scenarios definition plays a relevant role in tsunami hazard assessment and emergency preparedness for evacuation planning. A series of highly destructive major tsunamigenic events occurred during the last two decades, have given valuable insights about the geological and hydrodynamical processes of tsunami. There is a current lack of knowledge in predicting future impacts of tsunami events, despite the improvements on the understanding of megathrust earthquakes source dynamics and the technical advances of real-time monitoring of tsunami propagation. One the most relevant complexities lies in the lack of predictions of a plausible rupture pattern of tsunamigenic earthquake source. The northern Chile seismic gap constitutes an earthquakes natural laboratory due to their long-term seismic quiescence since the 1877 M_w 8.7 earthquake. Currently, seismic monitoring and geodetic models indicate a high seismogenic potential of a future M9 event with a slip deficit ~20 m, including a significant tsunami threat. In this work, we apply a deterministic-stochastic multi-scenario approach to construct a finite set of plausible non-uniform earthquakes rupture patterns. We evaluate the tsunami hazard level in the city of Mejillones, where converges numerous industrial complexes and mining warehouses. Additionally, the historical reports of 1877 M_w 8.7 earthquake show a massive inundation in Mejillones, including an estimated maximum tsunami flow-depth of ~21 m. Following K-L expansion technique, we construct a set of ~1000 non-uniform stochastic earthquakes scenarios with a magnitude range of M_w 8.7 to M_w 9.0. The obtained seismic sources were used as input to model the tsunami inundation under a non-hydrostatic scheme, to extract high-resolution data for flow-depth, sea level elevations and arrival times. The expected credible worst-case scenario for Mejillones is a M_w 9.0 earthquake, covering a total area of 5.36 km² of the city, with a maximum flow-depth of ~33 m and arrival times of ~15 minutes. The combined use of high-resolution tsunami modelling and novel techniques to construct an earthquake scenarios database can play a relevant role to anticipate more accurately the impacts and damage of a credible worst-case scenario to implement an efficient tsunami preparedness.