Deep Earthquakes

Below depths of 60-100 km, pressure and temperature conditions should inhibit the brittle behavior necessary to generate earthquakes, and yet around 1/4 of all earthquakes occur below these depths.  Many mechanisms have been proposed to explain this deep seismicity based upon laboratory and theoretical studies.  My work on this subject evaluates these different mechanisms based upon the rupture behavior of the largest deep earthquakes.










Figure 1: (Left) Number of earthquakes with respect to depth.  Darker bars are deep earthquakes.  (Right)  High-frequency energy release of a Mw 7.4 deep earthquake that occurred in Hindu Kush on March 3, 2002.  High-amplitude sub-events are separated by 75 km and 8.5 seconds suggesting the activation of multiple fault segments, and dynamic triggering of the second sub-event by seismic waves from the first sub-event.