THE 1995 COLIMA-JALISCO, MEXICO, EARTHQUAKE (MW 8) - A STUDY OF THE RUPTURE PROCESS

In this study we map rupture characteristics of the great, shallow, th rust earthquake of October 9, 1995 which caused extensive damage to th e coastal towns of Colima and Jalisco. To isolate the earthquake ruptu re details, we deconvolve surface waves with two empirical Green's fun ctions, the aftershock of October 12, 1995 (Mw 5.9) and the foreshock of October 6, 1995 (Mw 5.8), from the corresponding mainshock records. Specifically, we use a spectral water-level deconvolution to obtain 8 0 Apparent Source Time Functions (ASTF) at 62 stations (Rayleigh and L ove waves). Durations of the ASTF, as a function of azimuth indicate t hat the rupture propagated toward N70 degrees W. The duration of the S ource Time Function (STF) is around 62 s with a large pulse at 45 s. T o map the main characteristics of the rupture, we use an inverse Radon transform of the ASTFs, assuming a ribbon fault-model aligned in the direction of the rupture propagation. Our analysis indicates that the rupture initiated about 20 km offshore of Manzanillo and propagated al most unilaterally for 150 km towards N70 degrees W, with an average ru pture velocity of approximately 2.8 km/s. The earthquake was a composi te of three significant subevents, the largest occurred 45 s after the initiation of the rupture and was located about 100 km away. This res ult is in good agreement with the inversion of deformation data, measu red with GPS [Melbourne et al., 1997].