Opposing gradients of permanent strain in the aseismic zone and elastic strain across the seismogenic zone of the Kodiak shelf and slope, Alaska

An industry‐acquired seismic reflection line from the Aleutian Arc to the Alaska Trench was prestack depth‐migrated and further constrained with wide‐angle ocean bottom hydrophone seismic velocity data and swath mapping. From the seismic reflection image, individual thrust slices, the backstop, and the forearc basin were resolved sufficiently well to balance the section. Tectonic shortening and age estimates provided rates of permanent contraction in five discrete segments over ∼150 km during the past 3 Myr. About 70% of the plate convergence is measured as contraction across the ∼40‐km‐wide Neogene accretionary prism which composes less than 10% of the forearc. Permanent contraction is minimal above the 1964 Alaska earthquake aftershock zone indicating dominently elastic strain. Since elastic strain is poorly recorded in the geological record, it was approximated from the historical record of the 1964 Alaska earthquake. The 1964 coseismic vertical deformation displays an inverse pattern to the permanent strain, consistent with the earthquake cycle concept. Elastic deformation is dominant beneath the shelf and upper slope, rapid permanent deformation is concentrated beneath the lower slope, and a transition between them occurs beneath the middle slope.