Inversions of Geodetic Data for Rotation Pole and Deformation Mechanism at Subduction Zones: Applications to Cascadia, Sumatra, and Alaska

We use horizontal and vertical geodetic data to perform linear inversions at the Cascadia subduction zone in Washington and Oregon, the Kenai Peninsula in Alaska, and the Sumatra subduction zone. The total velocity field is viewed as the superposition of plate convergence deformation and rigid block motion, and we use a linear inversion method that simultaneously solves for both of these components. For the deformation component we assume either an elastic half-space dislocation (EHSD) model, in which case we solve for the slip deficit rate, or a finite elastic plate model, in which case we solve for the rate of stress accumulation along the plate boundaries. We also solve for the rotation pole(s) of predefined blocks, which typically represent forearc slivers. We approximate the continuous distribution of deformation sources with a finite number of impulse response functions and use inversion techniques appropriate for highly underdetermined problems, thus allowing a very fine discretization of the deformation sources. We compare the results obtained using EHSD models and finite plate models, and we also evaluate the conditions under which the complete three-dimensional problem may be reasonably approximated by a series of two-dimensional profiles. Preliminary modeling results indicate that block rotations represent a significant portion of the overall deformation field in Cascadia and Sumatra, but are less important in Alaska.