Coseismic subduction zone strain-release as a constraint for slab dynamics

Slab rheology and the lateral viscosity variations in the ambient mantle in subduction zones are key controls on upper mantle dynamics but still poorly constrained. Mantle flow modeling puts seismic strain-rates into the context of regional subduction dynamics and global mantle circulation, and our goal is to arrive at a globally consistent model of plate motion and slab deformation. We analyze the co-seismic strain-rates that are recorded by the global centroid moment tensor (gCMT) catalog in conjunction with the temperature anomaly distribution and slab morphology that can be inferred from seismic tomography. Our analysis of gCMTs confirms the global patterns that were established by Isacks and Molnar (1971) where intermediate depth in- slab extension merges into deep in-slab compression in some, but not all subduction zones. The large increase of seismic data over the last tens of years allows spatial refinements of Kostrov summations. Those show ubiquitous, second-order complexity on regional scales, perhaps due to effects such as slab tears. We find that no simple kinematic model can provide an adequate description of this diversity in strain patterns. Our fluid dynamical modeling builds on the 2-D analysis of Vassiliou & Hager (1988) and regional 3-D studies by Billen & Gurnis (2003); we strive to explore both regional and global fluid-dynamical effects such as slab deflection and folding at 660~km, effects of a higher viscosity lower mantle and weak mantle wedge, and the role of depth-dependent slab strength. A better understanding of the interaction of the large-scale flow with subducting slabs as imaged by seismicity motivates improved 3-D models. Those can provide background information for what slab deformation states are predicted based on global plate dynamics, and what component of strain-release may be indicative of regional, possibly transient tectonic effects.