Large station displacements observed from Imperial Valley global positioning system (GPS) campaigns are attributed to the November 24, 1987, Superstition Hills earthquake sequence. Thirty sites from a 42‐station GPS network established in 1986 have been reoccupied during 1988 and/or 1990. Displacements at three sites within 3 km of the surface rupture approach 0.5 m. Eight additional stations within 20 km of the seismic zone are displaced at least 10 cm. This is the first occurrence of a large earthquake (MS 6.6) within a preexisting GPS network. Best‐fitting uniform slip models of rectangular dislocations in an elastic half‐space indicate 130 ± 8 cm right‐lateral displacement along the northwest‐trending Superstition Hills fault and 30 ± 10 cm left‐lateral displacement along the conjugate northeast‐trending Elmore Ranch fault. The geodetic moments are 9.4 × 1025 dyn cm and 2.3 × 1025 dyn cm for the Superstition Hills and Elmore Ranch faults, respectively, consistent with teleseismic source parameters. The data also suggest that postseismic slip along the Superstition Hills fault is concentrated at shallow depths. Distributed slip solutions using singular value decomposition indicate near uniform displacement along the Elmore Ranch fault and concentrated slip to the northwest and southeast along the Superstition Hills fault. A significant component of nonseismic secular displacement is observed across the Imperial Valley, which is attributed to interseismic plate‐boundary deformation.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.