Focal mechanism, magnitude, and finite-fault rapid estimation using the elliptical patch method in Chile

Abstract

Nowadays, most fast, automatic algorithms estimate the magnitude and location of earthquakes assuming a point-source approximation that might produce large errors in the predicted shaking. In this study, using a kinematic approach, we modeled the fault plane as an elliptical patch with a Gaussian slip distribution to perform a rapid estimation of the finite fault, focal mechanism, and moment magnitude. We implemented this finite-fault kinematic inversion using data from the Centro Sismologico Nacional of the Universidad de Chile. We used near-field data, up to 600 km from the epicenter, mostly from accelerograms and a few nonsaturated broadband records. By considering data up to 5 min from the origin time, we are able to retrieve relevant source parameters within 10-15 min from the occurrence of the event. This elliptical patch method (EPM) successfully resolves the source parameters for 45 moderate-to-large events, from 2013 to 2017 (magnitudes ranging from 6.0 to 8.3). These results encourage the use of the EPM in the rapid response to moderate-to-large earthquakes in subduction zones.