Slip Distribution of the Chilean Earthquake of March 3, 1985 on the Central Chile Seismic Gap

Abstract:

We studied the slip distribution of the Mw 7.8 Valparaiso earthquake of 3 March 1985. This earthquake occurred within a region of previous great historical subduction earthquakes and may have filled a gap of high seismic potential on the Nazca-South America plate boundary. The event has been the subject of several publications on source rupture mechanism that has been characterized by a series of multiple events, and the seismic moments estimated vary with the frequency content of the data utilized. Some of these studies found that the inferred maximum slip obtained by from wide-band analysis is too small and would suggest that a future large-slip event has yet to occur in the area (Mendoza et al., 1994). We applied a linear scheme finite-fault waveform inversion to the teleseismic P waves, allowing a variable dislocation rise time for every point source on the fault. The results show that rupture propagated 100 km southward, with a total duration of 70 seg. Most of the slip is concentrated on two patches at depth between 25 and 45 km. The patch of maximum slip is near of nucleation zone. After we inverted the earthquake, we modeled the tsunami for this event. We compare run-up and tide gauges observations with the synthetic ones. The result confirms that the slip patch is located between 25 and 45 km depth. This suggests that the source did not break the upper part of the interplate contact zone. Recently studies demonstrated that the 1730 earthquake with epicenter offshore Valparaíso was the largest of the historical events occurred in Central Chile region. It affected a zone stretching for more than 1000 km along the coast from Copiapó to Concepción and caused great damage in Santiago and Valparaíso. It produced a large tsunami that especially affected Valparaíso and Concepción. Therefore, a repeat of this event in the future is not excluded, and thus this region should be carefully surveyed.