Horizontal deformation associated with the Loma Prieta earthquake

Abstract

Co-seismic horizontal displacements for the 1989 Loma Prieta earthquake were derived from preseismic triangulation/trilateration observations and post-seismic GPS observations. As part of this process, the empirical model entitled TDP-H91 was applied to “correct” the preseismic measurements for the crustal motion that occurred during the seven decades spanned by these data. These newly derived displacements were combined with previously documented geodetic results to generate a dislocation model for the earthquake. Our preferred model consists of a vertically segmented rupture surface represented by two rectangles that share a common edge at a depth of 9 km. The upper rectangle dips 90° and the lower rectangle dips 70°SW. Via a trial-and-error technique, the following estimates were found for the remaining parameters: strike = 134.4 ± 0.7°, fault length = 32.4 ± 0.7 km, upper depth = 4.8 ± 0.1 km, lower depth = 15.1 ± 0.3 km, right-lateral strike slip = 1.86 ± 0.06 m for the upper rectangle and 1.96 ± 0.13 m for the lower rectangle, and thrusting dip slip = 1.06 ± 0.06 m for the upper rectangle and 2.30 ± 0.18 m for the lower rectangle.