Deep-Focus Earthquakes in America

Abstract

This paper is based on detailed catalogues giving epicenters, origin times, and hypocentral depth for a large number of deep shocks.1 In the Americas, shocks at very great depth (in excess of 600 km.) have been found in only four small areas east of the Andes (see figure 1). No shocks are known to have occurred in America at depths between 300 and 600 km. Shocks between 50 and 300 km. deep ("intermediate" shocks) are frequent along the Andes from 40° S to Colombia. South of 20° S, shocks at depths of 50-140 km. are found nearer the coast than those at depths of 150-290 km. Numerous shocks at the larger depths occur between 20° and 24° S, near 67° W; but this high activity breaks off abruptly to the south, coincidently with the breaking off of the eastern Andean structures.