Theory of warping of southern Alaska before Alaska Earthquake, 1964

Abstract

Elements of plate tectonics and engineering beam theory are used to calculate preearthquake vertical and horizontal displacements for southern Alaska. Duration of the preearthquake time period is from the time immediately prior to the 1964 earthquake to the time immediately after the next youngest major earthquake, which occurred approximately 1350 yr earlier. The formula for computing displacements considers an axial load and shear force that are applied to the toe of the thrust sheet overlying the Patton Bay fault and also considers lithostatic and elastic resistance of the underlying medium to deflection of the overlying thrust sheet. Results are compatible with observed preearthquake displacements. Calculated preearthquake displacement shows a seaward zone of subsidence, a central zone of uplift, and a landward zone of slight subsidence. By assuming elastic rebound during the 1964 earthquake these results closely predict observed earthquake displacements, including the secondary zone of slight uplift along the Alaska range.