Space-Time Clustering of Large Thrust Earthquakes along the Mexican Subduction Zone: An Evidence of Source Stress Interaction

Abstract

The spatiotemporal plot of epicenters of large ( M s ≥6.9) subduction earthquakes in Mexico (1900 to present day) suggests that these earthquakes cluster in space and time. In this work we test the hypothesis that the coseismic stress transfer may lead to this clustering. For the analysis we estimate the spatial extent of the coseismic Coulomb stress change for these large events and then perform a statistical analysis using the χ 2 goodness-of-fit test for the interevent time intervals. We find that there are, at least, two groups of time intervals where the observed frequencies are much higher than that expected from a Poisson model, indicating a bimodal pattern. For the first mode, the observed frequencies for the 0- to 5-year interval becomes about 2.1 times the expectation, with a probability of occurrence of about 30%. These results show that large thrust Mexican earthquakes between 1900 and 2003 are clustered in space and time probably due to stress interactions among them. The second mode includes the time interval of 30–50 years. In the interval of 30–40 years, the observed frequencies become about 1.7 times the expectation and about 1.2 times the expectation for the 40- to 50-year interval. This second mode could be associated with a reloading interval of tectonic stress due to the plate convergence and appears consistent with the long-term recurrence periods of large thrust earthquakes in the Mexican subduction zone.