Deep focus earthquake - Definition and Overview

A deep focus earthquake is an earthquake that occurs at depths of 600 to 700 km beneath the Earth's surface. Their cause is still not entirely understood since subducted lithosphere at that pressure and temperature regime should not exhibit brittle behavior. They are believed to be associated with a catastrophic phase change as large portions of slab or slab-entrained material convert from a spinel structure to a more compact perovskite structure.