Destructive upper-crustal earthquakes of Central America since 1900

Abstract

Abstract We have compiled a catalog of 51 destructive upper-crustal earthquakes in Central America since 1900. An event is included if it caused casualties or heavy damage of Modified Mercalli (MM) intensity ≧ VII. All events larger than magnitude Ms 5.7 are found to be destructive. We believe the catalog is complete for events of Ms ≧ 6 along the volcanic front. The catalog includes estimates of epicentral coordinates, depth, magnitude, and casualties for all events and presents MM intensity VII contours for most events. Data in this catalog place severe constraints on the spatial, temporal, and magnitude distribution of destructive upper-crustal earthquakes in Central America. The catalog contains 30 events of Ms ≧ 6. Depths of well-constrained mainshock hypocenters range from 5 to 15 km. The most striking feature of the catalog is the spatial alignment along the volcanic front of 23 of the 30 events; volcanic-front earthquake-source mechanisms for such events show east-west tension and are compatible with a model of the volcanic front as a zone of right-lateral strike-slip faulting. Volcanic-front earthquake magnitudes do not exceed Ms 6.5, except in southeastern Guatemala where they reach Ms 6.9; maximum earthquake magnitudes are apparently related to the distance between adjacent Holocene volcanic centers. Destructive events occur at offsets in the volcanic chain as isolated mainshock-aftershock sequences. However, within linear segments, destructive earthquakes have a strong tendency to cluster and are often preceded by significant foreshock activity. Although the volcanic front is the locus of both destructive earthquakes and volcanism, we find no temporal correlation between the two. Of the seven events of Ms ≧ 6 that did not originate near the volcanic front, six originated near the transcurrent Caribbean-North American plate boundary, including the Ms 7.5 Guatemala earthquake of 1976. Along the volcanic front, destructive upper-crustal earthquakes have occurred at a rate of about one event every 212 years during this century, much more frequently than along either the Caribbean-North American plate boundary or the subduction zone. In Central America since 1900, about 17,000 people have died from volcanic-front earthquakes, but only about 2000 people are known to have died from subduction-zone earthquakes. Although subduction zone earthquakes can have larger magnitudes and produce more widespread damage, destructive volcanic-front earthquakes pose the greater hazard because they are more frequent and originate much closer to the bulk of Central America's population, which is concentrated along the volcanic front.