Deep earthquakes happen where sinking slabs deform at the fastest rates.

Simulations of sinking tectonics plate provide new evidence that like earthquakes at the surface, deep earthquakes happen where the rate of deformation is the highest. The new results published in Sciences Advances show that in models with stiff (high viscosity) sinking plates, localized yielding occurs in regions of bending and buckling. The depth distribution of these fast deforming regions is very similar to the depth distributions of deep earthquakes.

A UC Davis new article by Becky Oskin provides a nice overview of the results.