Unraveling the effect of convergence obliquity on overriding-plate deformation and strain partitioning in subduction zones

Nestor G. Cerpa , Serge Lallemand, Arnauld Heuret

The subduction of an oceanic plate causes deformation of the overriding plate, from the forearc to the back-arc regions. Over years, to address the physical controls on such a deformation, various compilations on active deformation have been made, mixing various types of datasets including fault-slip rates, focal mechanisms and geodetic motions. The growing amount of available data now allows for the construction of consistent compilations in terms of data types. Here, we present a database for the kinematics of subduction zones which includes that of the overriding-plate deformation, consistently based on geodetic data. The database describes the 2-d (trench-normal and trench-parallel) motions of arc blocks for ~90% of active subduction zones, through the magnitude (vd) and the deformation-obliquity angle (Ovd) between the blocks and the upper plate (undeformed interior of the overriding plate). We classify subduction zones into 4 dominant strain classes (compressional, strike-slip, extensional, and neutral), and into up to 8 classes including intermediate regimes. Focusing on the strike-slip strain class, we show that a non-negligeable trench-parallel motion is a widespread feature of active subduction zones. The convergence obliquity exerts, however, a contrasting effect on Ovd, thereby suggesting a limited effect on strain partitioning at oblique subduction zones. On another hand, Ovd shows a positive correlation with slab dip, where low and high values are associated with compression and extensional classes, respectively. Finally, we provide revised estimations of subduction rates, allowing for instance refined estimations of the thermal parameter, which will permit future comparative investigations on subduction dynamics and tectonics