Source process and stress change associated with the 11 January, 1997 (Mw=7.1) Michoacán, Mexico, inslab earthquake

We study the source characteristics and the associated coseismic stress change of the January 11, 1997 Michoacán earthquake, based on teleseismic, regional and near-source recordings. This event was located just beneath the ruptured zone of the 1985 Michoacán thrust event. From the inversion of teleseismic recordings, we obtain a nearly-vertical faulting at 35 km depth, a total source duration of 15 sec, a moment magnitude of Mw=7.1, and a mean rupture velocity of 2.8 km/sec. An analysis of teleseismic and local seismograms shows that the rupture had a strong directivity to the southeast, with a rather complex source-time function with two main subevents and a total duration of 13 sec. The dislocation distribution obtained from 2D kinematic linear inversion, using both local strong motion and broad-band teleseismic data, shows a complex rupture pattern with the main seismic moment release occurring in the southwest portion of the fault. A comparison between the coseismic Coulomb failure stress change during the main shock, and the location and mechanism of the aftershocks, suggests that post-event seismicity may have been triggered by the stress changes due to the main event.