TESTING THE LINK BETWEEN PLATE BOUNDARY OBLIQUITY AND INTERPLATE DEFORMATION

Oblique plate boundaries cause strain partitioning in plate boundary zones. The separation of the relative plate motion into a normal component perpendicular to the plate boundary and a shear component parallel to the boundary, causes permanent deformation along discrete faults or transpression/transtension affecting a wider area. Strain partitioning is important for understanding plate boundary processes, including long-term deformation, interseismic coupling at the plate boundary interface, volcanism, and the mass and energy transfer between the adjacent plates. Although most plate boundaries experience some degree of oblique relative plate motion, the extent to which the obliquity controls deformation has not been rigorously tested.

I test the effect of obliquity on long- and short-term deformation in the plate boundary zones using global datasets of present-day stress fields, geodetic strain rates, and mantle seismic anisotropies. Orientations and spatial distributions are transformed into a coordinate reference system described by the relative motion of adjacent plates. This removes angle and area distortions and allows for statistical evaluation of correlations. The results indicate strong linear correlations between plate boundary obliquity, the orientation of stress and strain fields, and the vorticity of interseismic geodetic strain. Moreover, spatial correlations of the stress field perturbations, active volcanism, and the patterns of the mantle anisotropy indicate coupling between the crust and the mantle lithosphere. Thus, obliquity predicts the orientation, the magnitude and the sense of lateral interplate deformation, even for plate boundaries with relatively low obliquity and no predominant discrete strike-parallel faults. It controls interplate deformation, where along-strike changes in the angle between the relative plate motion and the boundary result in lateral deflections of the stress, causing deformation along strike-parallel or pre-existing faults.