Revisiting the 1959 Hebgen Lake earthquake using optical image correlation; new constraints on near‐field 3D ground displacement

Near-field surface displacement measurements allow us to quantify the on- and off-fault proportion of earthquake-related deformation. The Hebgen Lake earthquake was a large normal event with a complex surface rupture, which broke across mountainous terrain. This study takes advantage of high-resolution historical aerial stereo-imagery to measure three-dimensional displacement from correlation of the orthorectified pre- and post-earthquake image mosaics. The results reveal new strike-slip ruptures which are possibly associated with the aftershocks from 18th August 1959. These structures likely reflect internal block deformation induced by the complex geometry of the mainshock. Additionally, comparison of our results with the existing displacement data shows that the optical image correlation-derived offsets often exceed the field measurements by >50%. We attribute this difference to inelastic off-fault deformation.