To help teachers respond to questions such as these, this EduQuakes column is focused on earthquake depth, and the EduPhase section treats pP . Although not a comprehensive survey of hypocentral depth, at least it provides a starting point for students to learn about the nagging problems with hypocentral depths in global seismicity catalogs.
Earthquakes occur within the Earth, and the depth of rupture initiation is the hypocentral depth.
There are a few funny spots around the world with deep earthquakes and no subduction zone, but most seismologists think that geologically recent subduction explains these events. There are two answers to this question. The scientific answer is that it depends on the tectonic environment. In regions of the world that can be characterized as spreading, rifting, volcanic, and transform faulting, detailed seismological studies show that most earthquakes have a hypocentral depth of 15 km or less. In subduction zones, most seismicity occurs along the plate boundary down to a depth of about 40 km.