GPS based tectonic analysis of the Aleutian arc and Bering plate

Abstract

Global Positioning System (GPS) measurements enable a quantitative analysis of tectonic deformation in the Aleutian Islands, Alaska. We construct elastic deformation models to calculate coupling on the subduction interface and the interseismic strain recorded at stations throughout the Aleutian arc. Using a grid-search inversion procedure, we determine an arc translation velocity for each region of the arc, revealing south to southwest motions of 4 to 14 mm/yr. In the central Aleutians, there is good agreement between areas of high coupling and areas of large moment release in major seismogenic events. We have combined modeling results from the Aleutians with direct measurements of station velocities of sites in western Alaska and the Bering Sea islands to test the hypothesis of a clockwise rotating Bering plate. The Bering Sea area including the Aleutian arc and western Alaska is fit by an Euler pole located at 42.5°N, 121.3°E with an angular velocity of 6.0°/my, relative to stable North America. The Bering plate's eastern boundary appears to be related to left lateral faulting in interior Alaska as clockwise rotation of the plate results in south-southwest motion relative to the North American plate. The Bering plate's interaction with a counter-clockwise rotating southcentral Alaska block may be responsible for the decreased slip-rate on the western Denali fault. Thrust earthquake slip azimuths expose a systematic discrepancy with Pacific-Bering plate convergence direction. A simple model of slip partitioning and GPS measurements reveal that slip partitioning is present in the forearc throughout the arc but only develops in the back arc west of Amchitka Pass.