Aleutian Strain Events: Observations and Interpretation

Abstract

Summary Static dislocation theory has been applied to interpret a large aseismic strain event observed on strainmeter records from the central Aleutian Islands, and to interpret permanent sudden changes in earth strain that accompanied an Aleutian earthquake. In this interpretation, the aseismic strain adjustment is assumed to be caused by an episode of fault creep occurring in the region of the instruments. The model assumes that the faulting process can be suitably approximated by a rectangular plane dislocation of constant offset occurring in a homogeneous, isotropic, elastic half space. Fault depth, dimensions, dislocation offset, and orientation are parameters which specify strain changes. An iterative least-squares inversion technique has been applied to find the fault parameters that allow a best fit to the data. A solution in reasonable agreement with both the aseismic strain changes and the theory of Aleutian plate tectonics can be found. However, this agreement is obtained only if results obtained by considering the earthquake are used to correct the aseismic solution. It appears that observed strains are too large by an order of magnitude.