Resolution analysis of the tsunami generated by the 2014 Mw 8.1 Pisagua earthquake using a simple slip model

Abstract:

Northern Chile has been identified as a likely mature seismic gap that spans approximately from Mejillones peninsula to Ilo in southern Peru. The 2014 M_w 8.1 Pisagua earthquake broke the middle segment, and coseismic slip models show that the slipped zone occurred in the intermediate to deeper portion of the megathrust fault interface between the downgoing and overriding plate. The tsunami generated by the Pisagua earthquake caused minor impact along the Chile shore, and, for instance, at the Iquique tide gauge, the leading wave reached an elevation of about 1.8 m and a depression of ~2.5 m. In the present work, we would like to address the tsunami generation, propagation and runup associated to the 2014 Pisagua earthquake. This work aims to understand, from a numerical point of view, why this event did caused a minor tsunami, to test the feasibility to model correctly the sea water level at DART buoys and local tide gauges, and to estimate the sensitivity of the runup amplitudes to earthquake source parameters. We collect published coseismic slips for this earthquake and used a proposed coseismic slip model obtained using seismological data. Assuming an elastic halfspace and the linear superposition principle, the static displacement field from these earthquake slip models was computed using the Okada's formula for a point-source and we use the vertical displacement computed at the seafloor as initial condition to propagate the tsunami. Preliminary results shows that major differences are observed in the near-field. Obtaining the static seafloor deformation we can immediately obtain an estimation of the maximum runup by using a multisloping beach model which allow us to understand how well-conditioned is the zone for a large tsunami. In terms of earthquake source, most of slip models show a single asperity that one can model as an elliptical slip crack. To test the sensitivity of the runup and water elevation to earthquake source parameters, we use a simple earthquake model to describe the coseismic slip associated to the 2014 Pisagua earthquake. By varying the crack location and fault geometry, we are currently estimating the variability of runup distribution and seawater elevation in the near-field.