How Much Surface Deformation Results from Slab Processes Rather than Surface Plate Tectonics?

The largest deep focus earthquake yet recorded (Mw 8.3) occurred 24 May 2013 at 607 km depth beneath the Sea of Okhotsk. Unlike past deep focus events, this earthquake caused significant displacements at the surface, which were measured using continuous GPS sites in Kamchatka, the Kuril Islands, Komandorsky (Russian Aleutian) Islands, and adjacent areas of the Russian Far East (Steblov et al., this meeting). The surface displacements can be explained by extensional faulting using either the GCMT primary or auxiliary fault plane consistent with the seismic moment magnitude, although the GPS displacements do not constrain the rupture area or slip independently. Although the largest measured displacements for this event are only ~15 mm, this raises the question of how much does deformation of the slab contribute to the surface displacement/velocity field? For example, is there an 'interseismic' signal associated with the stress/strain buildup prior to these events? If there is no equivalent to 'elastic rebound' for such events, then each large deep focus earthquake must produce permanent, although every long wavelength, strain of the surface plate. Like other deep focus earthquakes, this event represents deformation within the slab long after subduction. Intermediate depth earthquakes also result from slab deformation. Although plate tectonics is responsible for putting the slab in this situation, and the forces acting on the slab influence plate motions, the details of how the slab deforms have generally been thought to be irrelevant for measurements of surface plate motions. In this presentation I will quantify the global surface deformation rate from intermediate and deep focus events and explore the consequences of this deformation for geodetic estimates of plate motion and plate boundary deformation. Predicted coseismic displacements based on the GCMT moment tensor.