Tsunamigenic potential of outer-rise normal faults at the Middle America trench in Central America

Abstract

The Middle America trench is formed by the subduction of the Cocos and Rivera plates under the Caribbean and North American plates. The subduction interface presents low coupling in Central America showing its seismicity a high frequency of outer-rise normal fault earthquakes. These outer-rise earthquakes are generated on the inherited structures of the seafloor-spreading fabric during the subducting plate bending. We analyze focal mechanism data in combination with the available structural data of the outer-rise normal faults in order to constrain the rupture characteristics of the outer-rise normal earthquakes. A new empirical scaling relationship is developed to define earthquake magnitudes from normal fault dimensions in the outer-rise context. We numerically model the tsunami wave propagation due to the worst outer-rise tsunamigenic source in the area to estimate its damaging potential. Wave elevations higher than 2m are common at the coast in front of the fault extent, with maximum wave elevations of 8m. The capability of these faults to generate ocean-wide tsunamis is low, however, they can produce significant tsunamis locally.