Co-seismic deformation of deep slabs based on summed CMT data

We assess the co-seismic deformation inferred from earthquake moment tensor solutions for subducting slabs at depths greater than 50km globally. We rotate each moment tensor into a local slab reference frame, then sum tensors within 50km depth bins to approximate long term deformation characteristics. This builds upon previous analyses by using the up-to-date global Centroid Moment Tensor catalog, incorporating a more complete slab geometry, and focusing on the 3-D aspects of slab deformation. Results show a general consistency with Isacks and Molnar (1969), who found that most slabs can be divided into intermediate-extensional, intermediate-extensional-deep-compressional, and intermediate to deep-compressional categories. Exceptions to these three categories can be related to slab bending in the top 100km, plate convergence that is oblique to the trench normal direction, and regions of higher focal mechanism heterogeneity. The regions of higher focal mechanism heterogeneity appear where there are along-strike changes in slab geometry and/or evidence of double-seismic zones. We find that the sense of deformation in the intermediate strain axis direction is opposite to that of the down-dip direction, in agreement with Kuge and Kawakatsu (1993). By quantitative comparison to numerical models of global mantle flow, we show that these observations are consistent with deformation of viscous slabs responding to their own negative buoyancy and an upper to lower mantle viscosity increase.