Evidence for and implications of a Bering plate based on geodetic measurements from the Aleutians and western Alaska

Abstract

Global Positioning System (GPS) measurements are used to examine the hypothesis of a clockwise rotating Bering plate. Originally proposed on the basis of seismicity, the Bering plate encompasses the Bering Sea, western Alaska, and the Aleutian Islands. GPS measurements from the Bering plate's interior show south to southwest motions of 3-5 mm/a (where a is years). We construct elastic dislocation models to determine the spatial distribution and intensity of locked patches on the Aleutian subduction interface. We use these to remove interseismic strain from the GPS observation and determine an arc translation velocity for each region of the Aleutians, revealing south and southwest motions of 4-8 mm/ a. We combine the arc translation rates with measurements from the Bering plate's interior sites and estimate the Euler pole for the Bering plate relative to North America to be located at 42.5°N, 121.3°E with an angular speed of 6.0°/Ma. The clockwise rotation of the Bering plate may cause left lateral faulting in interior Alaska. The Bering plate's interaction with south-central Alaska may be responsible for the decreased slip rate on the western Denali fault and for contraction across the central Alaska Range. We analyze slip partitioning along the Aleutian arc on the basis of both GPS measurements and slip azimuths of thrust earthquakes and find a systematic discrepancy between plate convergence direction and slip azimuths. We conclude that slip partitioning in the back arc only develops west of Amchitka Pass, whereas slip partitioning in the fore arc is present throughout the arc. Copyright 2008 by the American Geophysical Union.