Geologic setting of some destructive earthquakes in Central America

Abstract

Most destructive earthquakes in Central America are either shallow earthquakes of moderate size (4 ≤ M ≤ 7) that occur in the volcanic belt or large shallow earthquakes (M > 7) that occur along the inclined seismic zone. Each of these classes of earthquakes, as well as the locations where population centers have developed, appears to be spatially controlled or influenced by Quaternary structures. This study examines the relationships between destructive earthquakes and Quaternary tectonics and uses this information to develop qualitative estimates of seismic hazard. Quaternary structures in the volcanic belt of Central America are linked to the zone of plate convergence by transverse breaks that segment the overriding slab and the underthrust slab. The surface expressions of these breaks are transverse structural depressions. Longitudinal structural depressions coincide with lines of active volcanos. Moderate-size shallow earthquakes in the volcanic belt occur within the grid of transverse and longitudinal structural depressions. Many of these shallow earthquakes occur near the lines of active volcanos or are associated with volcanic eruptions. The grid of structural depressions that localizes these earthquakes provides a topographically favorable urban site. Many cities have therefore been built in especially hazardous areas. Large shallow earthquakes that occur in the inclined seismic zone can be divided into two types: major earthquakes that have relatively small focal areas and short recurrence times and which cluster around transverse breaks in the arc, and great earthquakes that have large focal areas, cause great damage, are infrequent, rupture one or more segments of the arc, and have focal areas that end at transverse breaks. Most great Central American earthquakes occurred in two brief space-time progressions. During 1847–1851 great earthquakes ruptured the El Salvador, eastern Nicaragua, and two Costa Rican segments of the arc. During 1898–1902, the western Nicaragua segment, the three Guatemalan segments, and a segment in southeast Mexico were ruptured. The most probable areas for the next great earthquake are the El Salvador and central Costa Rica segments of the arc.