Surficial Slip Distribution on the Central Emerson Fault During the June 28, 1992, Landers Earthquake, California

Sally F. McGill, & Charles M. Rubin

Published March 10, 1999, SCEC Contribution #277

We present the results of our mapping of a 5.6-km length of the central Emerson fault that ruptured during the 1992 Landers earthquake in the southwestern Mojave Desert, California. The right-lateral slip along this portion of the rupture varied from about 150 to 530 cm along the main rupture zone. In some locations a total of up to 110 cm of additional right-lateral slip occurred on secondary faults up to 1.7 km away from the main rupture zone. Other secondary faults carried up to several tens of centimeters of left-lateral or thrust displacement. The maximum net vertical displacement was 175 cm, east-side-up. The sense of vertical slip across the main fault zone varied along strike, but in most cases it was consistent with the sense of vertical slip in previous earthquakes, as indicated by the locations of areas of older, uplifted, and abandoned alluvial fan surfaces. Although variations in surficial slip have been reported along previous strike-slip ruptures, our closely spaced slip measurements allow a much more detailed study of slip variability than was possible previously. We document variations in slip as large as l m or more over distances ranging from 1–2 km to a few tens of meters, suggesting that strains of the order of 10−1 may have occurred locally within the surficial sediments. The long-wavelength (kilometer-scale) variations in surficial slip may be influenced by fault geometry and perhaps by the thickness of unconsolidated sediments. The slip variations over shorter length scales (tens of meters) may be caused by variations in the proportion of the total shear that occurs on visible, brittle fractures versus that which occurs as distributed shear, warping or rotation. The variability of slip along the ruptures associated with the Landers earthquake calls for caution in interpreting geomorphic offsets along prehistoric fault ruptures.

McGill, S. F., & Rubin, C. M. (1999). Surficial Slip Distribution on the Central Emerson Fault During the June 28, 1992, Landers Earthquake, California. Journal of Geophysical Research, 104(B3), 4811-4833. doi: 10.1029/98JB01556.