Postseismic Strain Following the 1989 Loma Prieta Earthquake From GPS and Leveling Measurements
Journal of Geophysical Research, B, Solid Earth and Planets, v. 102, no.3 pp.4933-4955, March 10, 1997
Roland Burgmann (Department of Geology, University of California, Davis)
Paul Segall (Department of Geophysics, Stanford University)
Mike Lisowski (U.S. Geological Survey, Hawaiian Volcano Observatory)
Jerry Svarc (U.S. Geological Survey, Menlo Park)
Abstract
Postseismic deformation in
the five years following the 1989 Loma Prieta earthquake has been meas
ured with GPS and precise leveling. Post-earthquake velocities at
distances greater than ~20 km from the coseismic rupture are not
significantly different from those observed in the 20 years prior to the
earthquake. However, velocities at stations within approximately 20 km of
the rupture exceed pre-earthquake rates and exhibit unanticipated
contraction normal to the strike of the San Andreas fault system. A
combination of forward modeling and non-linear optimization suggests that
the observed postseismic deformations were caused by aseismic oblique reverse slip averaging 2.9 cm/yr on the San Andreas fault and/or the Loma Prieta rupture zone, and 2.4 cm/yr reverse slip along a buried fault within the Foothills thrust belt. The best-fitting sources of post seismic deformation are all located at depths of less than 15 km . We find no evidence for accelerated flow or shear below the Loma Prieta rupture in the first five years following the
earthquake. The inferred postseismic slip is likely to have been caused by the coseismic stress change updip of the 1989 rupture.
