Seismic Amplifications due to Topographic Effects in the North of Chile Coastal Scarp

Abstract:

The coastal scarp of the North of Chile is an important geomorphological feature, parallel to the oceanic trench. During the Mw 8.2 Pisagua earthquake, site effects were registered in the Alto Hospicio, Huara and Pozo Almonte councils, all locations placed above the high cliff. The observed site effects were not predicted by a previous seismic microzonation of the study area. The topographic effects due to the loss of soil confinement in the west edge of the scarp could be responsible of the seismic amplification registered.

In this work, a 2-D implicit Galerkin finite element model was constructed to estimate the effect of the seismic waves on the displacements experienced by the coastal scarp geometry. Our results indicate that vertical amplifications of the seismic waves are observed in the surface and in the scarp slope, with a range of influence from the edge of one hundred meters eastward, approximately. The displacement field found using this model is similar to the measurement made by GPS during coseismic displacement of typical subduction earthquakes. However, changes in the geometry of the finite element have a similar effect in the vertical displacement’s magnitude.

The model presented is, to the best of our knowledge, the first approximation to resolve the topographic effects in the seismic amplifications due the coastal scarp geometry in the andes?, where many assumptions have been used in order to simplify the results. In order to improve our results, further improvements to the model will be developed in the future, as the inclusion of relevant geological features.