Unraveling the Effect of Convergence Obliquity on Overriding-Plate Deformation and Strain Partitioning in Subduction Zones

Abstract

The subduction of an oceanic plate causes deformation of the overriding plate, from the forearc to the back-arc regions. Over the years, to address the physical controls on such 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 v_d and the deformation-obliquity angle (O_vd) between the blocks and the upper plate (undeformed interior of the overriding plate). We classify subduction zones into four dominant strain classes (compressional, strike-slip, extensional, and neutral), and into up to eight classes including intermediate regimes. Focusing on the strike-slip strain class, we show that a non-negligible trench-parallel motion is a widespread feature of active subduction zones. The convergence obliquity exerts, however, a contrasting effect on O_vd, thereby suggesting a limited effect on strain partitioning at oblique subduction zones. On the other hand, O_vd shows a positive correlation with slab dip, where low and high values are both associated with compressional and extensional classes, respectively. Finally, we provide revised estimates of subduction rates, allowing, for instance, refined estimates of the thermal parameter, which will permit future comparative investigations on subduction dynamics and tectonics.