Living Reference Work Entry

Encyclopedia of Complexity and Systems Science

pp 1-16

Date: Latest Version

Earthquakes, Deep

  • Cliff FrohlichAffiliated withInstitute for Geophysics, University of Texas at Austin Email author 
  • , Wei GanAffiliated withSchool of Earth Sciences and Resources, China University of Geosciences

Definition of the Subject

Deep earthquakes (DEQ) are earthquakes with focal depths between 60 and 700 km. They are of historical importance because their geographical pattern of occurrence provided critical information that helped confirm the theory of plate tectonics. Analyzing DEQ continues to be important because it provides important information about the structural, thermodynamic, compositional, and mechanical properties of the Earth’s deep interior. DEQ are mechanically puzzling because they occur under conditions where temperatures and pressures are too high to permit ordinary brittle fracture, the physical mechanism responsible for shallow earthquakes.


In the early twentieth century, the depth of ordinary earthquakes was an open question until observational studies in Japan (Wadati 1928) and elsewhere proved that focal depths ranged from the surface to almost 700 km. Scientists since have puzzled about the physical mechanism responsible for DEQ. Seismological observat ...

This is an excerpt from the content