Most- and Least-Likely Locations of Large to Great Earthquakes along the Pacific Coast of Mexico Estimated from Local Recurrence Times Based on b-Values

by F. Ramón Zuñiga and Max Wyss

Abstract

We mapped T_L and P_L (local recurrence time and local probability density, respectively) for M_max 7.2 earthquakes along the plate margin of the Pacific coast of Mexico in order to test two hypotheses. The first is that the minima in T_L (or maxima in P_L), extracted probabilistically from the frequency-magnitude distribution map asperities. The second hypothesis is that recurrence times for characteristic events are estimated more correctly by local recurrence times than by the overall recurrence times of the zone. Comparing these results to the observed recurrence times for events of M ≥7.0, we find good agreement. The coast of Guerrero between longitude west 100.5° and 101.5° and the segment off the coast of southern Chiapas show the shortest T_L estimated as about 20 yr; the location at longitude 98.5° (near the boundary of Guerrero with Oaxaca, the Ometepec segment) follows with estimates of about 30 yr as the next shortest T_L; along the coast of Guerrero, between 99° and 100.5° longitude, T_L is estimated as about 40 yr; and finally, in the segments off the Oaxacan coast near 95.7° and 97.7° longitude, T_L ranges from 40 to 60 yr. These volumes we define as asperities.

Long local recurrence times are observed for the areas offshore from the isthmus of Tehuantepec, on the Pacific plate off the coast of Guerrero, on land along the coast of most of Oaxaca, and along the northernmost 40 km of the Guerrero coast. If our ideas are correct, then major moment release should emanate from the volumes we defined as asperities, and relatively minor moment release should emanate from the volumes identified by the relatively long local recurrence times.

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