Localización hipocentral y mecanismo focal de algunos temblores fuertes de Costa Rica-Nicaragua

Abstract

Depth and focal mechanism for nine earthquakes (mb ≥ 5.3) that occurred in the pacific coast of Costa Rica-Nicaragua region are studied in detail. Depths, determined by the use of pP and sP phases, show to be 10-30 km shallower than those obtained from routine determinations based on first p-arrivals. Focal mechanisms obtained are typical of subduction zones. Tensional T-axis aline with the seismic activity which define the Benioff zone, indicating an increasing of its dipping angle with depth. Strike and dip of the pressure p-axis show stability; the direction of the p-axis, NE 30° SW, is similar to the direction of subduction of the Cocos plate beneath the Caribbean plate, which has been deduced to be N 40° E according to the average slip vector for the six shallower earthquakes. When a standard computer program to locate hypocenters that minimize first p-arrivals is used, depth determinations do not converge to a unique value.