Cinematic Source Inversion: Recent Normal-Faulting Earthquakes in Mexico

Arturo Iglesias, Bruno Hernandez, Victor Cruz, Shri Krishna Singh, Nikolai Shapiro, and Javier Pacheco
Instituto de Geofisica, UNAM, Ciudad Univercitaria, Coyoacan, DF 04510 Mexico

Abstract. We have inverted near-source and regional strong motion records to study the rupture history of two recent normal-faulting Mexican earthquakes (Tehuacan, 1999 Mw = 7.0. and Oaxaca, 1999, Mw = 7.5) with a frequency domain inversion scheme. The hypocenters and the origin times of the earthquakes were determined from local and regional data. We estimated the slip distribution on the fault and the associated rupture front propagation, as well as the rise time. The slip direction in the fault is assumed to be constant for a given geometry and equal to that reported from the Harvard CMT solution. For the Oaxaca earthquake, we have used a linearized inversion (Cotton and Campillo, 1995). Several inversions are carried out with different starting rupture parameters to test the uniqueness of the solution and to estimate the reliability of each parameter. Because of the lower data quality for the Tehuac n earthquake, the convergence of the linearized inversion was not satisfactory and we decided to implement a simulated annealing algorithm. A better solution with a lower misfit was obtained with this semi-global inversion. The results of our inversion show very similar slip distribution for both events: the rupture mainly propagated from ESE to WNW but also slightly downdip, with an average rupture velocity close to 3 km/s. The rise time (local duration of the rupture) ranges between 1 and 2s.