The majority of tectonic earthquakes originate at the ring of fire in depths not exceeding tens of kilometers.
Earthquakes occurring at a depth of less than 70 km are classified as 'shallow-focus' earthquakes(천발지진), while those with a focal-depth between 70 and 300 km are commonly termed 'mid-focus' or 'intermediate-depth' earthquakes(중발지진).
In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, deep-focus earthquakes(심발지진) may occur at much greater depths (ranging from 300 up to 700 kilometers). These seismically active areas of subduction are known as Wadati-Benioff zones. Deep-focus earthquakes occur at a depth where the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure.

유일하게 심발지진이 발생하는 장소는 섭입대(해구)가 있는 수렴경계부의 대륙쪽에서만 발생한다는 사실. 해구에서 대륙쪽으로 감에 따라 천발지진, 중발지진, 심발지진의 순으로 진원거리는 깊어지며(최대 700km까지만), 그 이상의 깊이에서는 지진발생 불가

우리나라(한반도)에서 발생하는 지진은 모두 천발지진임(그림 참조). 태평양판이 일본해구로 섭입하여발생하는 심발지진은 동해 먼바다까지만 영향.