A global survey of stress orientations in subducting slabs as revealed by intermediate-depth earthquakes

S U M M A R Y We examine a variety of mechanisms that have been proposed as contributors to the stress fields expressed as intermediate-depth seismicity in subducting slabs. To this end, we study principal stress orientations for a global data set of 1900 intermediate-depth focal solutions, determining the patterns of events characterized primarily by downdip compression, downdip tension, or neither. In regions dominated by downdip principal stresses, we find that conjugate stress axes exhibit preferential slab-normal orientations. Furthermore, we observe a clear trend of thermal control, in which colder slabs exhibit greater components of downdip compression while warmer slabs display greater downdip tension. In those regions not dominated by downdip principal stresses, a significant number of events exhibit lateral stresses in the form of subhorizontal principal axes in the plane of the slab. We conclude that the evidently complementary roles played by lithospheric age and subduction rate in constraining stress regimes support thermomechanical and petrological buoyancy models for control of intermediate-depth stresses. Moreover, observed lateral stresses support the traditional model of a squeezed ping-pong ball and stress patterns overall are consistent with some influence by reactivated fossil faults.