Strain accumulation in the Yakataga Seismic Gap, southern Alaska

Abstract

Strain accumulation in the Yakataga seismic gap has been estimated from the deformation of a 60 km × 40 km trilateration network surveyed in 1979–1980, 1982, and 1984. The contraction in the approximate direction (N19°W) of plate convergence is 0.19 ± 0.04 μstrain/yr, and there is a minor (0.07 ± 0.04 μstrain/yr) orthogonal extension. A significant right‐lateral shear (0.09 ± 0.02 μstrain/yr) occurs across a vertical plane striking N71°E. A simple dislocation representation of the plate interaction model proposed by Lahr and Plafker for the Yakataga seismic gap quantitatively accounts for the observed N19°W contraction and qualitatively accounts for the right‐lateral shear, the two strains being associated with the normal and transverse components, respectively, of the oblique convergence between the Yakutat block and the North American plate. The measurements are consistent with strain accumulation building up to a great thrust earthquake in the Yakataga gap. In addition, there is a suggestion of right‐lateral shear strain accumulation across the Contact fault, but the interval over which data are available is probably too short to prove such accumulation.