STRAIN ACCUMULATION ALONG THE LAGUNA SALADA FAULT, BAJA-CALIFORNIA, MEXICO

Strain accumulation observed over the 1978-1991 interval in a 30 x 100 km aperture trilateration network spanning the Laguna Salada fault is described by the principal strain rates 0.101 +/- 0.012 mu strain/yr N80 degrees E+/-2 degrees and -0.021 +/- 0.012 mu strain/yr N10 degrees W+/-2 degrees, extension reckoned positive. These strain accumulation rates have been corrected to remove coseismic effects of the nearby 1979 Imperial Valley (M = 6.5), 1980 Victoria (Baja California) (M = 6.4), 1987 Superstition Hills (M = 6.5), and 1987 Elmore Ranch (M = 5.9) earthquakes. The observed strain rates indicate extension at a rate of about 0.08 mu strain/yr perpendicular to the trend (N35 degrees W) of the Salton trough as well as a right-lateral tenser shear strain rate 0.05 mu strain/yr across it. The extension perpendicular to the trough is observed neither farther north near the Salton Sea nor farther south across the Gulf of California, However, Holocene slip on the Laguna Salada fault, about equal parts right-lateral and normal slip, is consistent with the observed strain accumulation. A simple dislocation model intended to explain the observed strain accumulation as a product of slip at depth on the Laguna Salada fault would require that the fault be listric.