Characterization of asperities of recent earthquakes in the subduction zone of Michoacán-Colima-Jalisco, Mexico

Abstract

Slip models of earthquakes of magnitude Mw greater than 7 occurring since 1980 in the Michoacán-Colima-Jalisco subduction zone were determined using P and SH waves recorded at teleseismic distances and a fault parameterization that allows a wide flexibility in rise time. The high slip areas of the different events do not overlap, forming an interlocking pattern of adjacent asperities separated by regions that could identify areas of major slip in future earthquakes. The systematic analysis of the earthquakes allowed an investigation of the uncertainties in the asperity properties. These uncertainties were determined using a simple sampling procedure where 300 independent inversions were run for each event taking into account possible errors in fault geometry, hypocenter depth and rupture velocity. The dimensions and maximum slip of the asperities appear to lie within the same range, which would imply the existence of relatively homogenous asperities in this portion of the plate interface. The rise times of the asperities are well constrained and scale with the size of the event. For Mw ~7.5 events the durations are ~5s and for earthquakes of Mw 8.0 the rise times are ~12s. The stress drops calculated for the asperities are less than 2.0 MPa, consistent with values estimated for subduction earthquakes in general. The results indicate that the parameter-sampling procedure offers an alternative for identifying the properties and uncertainties of asperities in subduction regions. Also, the results have important implications for the evaluation of the seismic potential and the development of earthquake scaling laws.