Surficial slip distribution on the central Emerson fault during the June 28, 1992, Landers earthquake, California

We present the results of our mapping of a 5.6-km length of the central Eme rson fault that ruptured during the 1992 Landers earthquake in the southwes tern Mojave Desert, California. The right-lateral slip along this portion o f 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-la teral or thrust displacement. The maximum net vertical displacement was 175 cm, east-side-up. The sense of vertical slip across the main fault zone va ried along strike, but in most cases it was consistent with the sense of ve rtical slip in previous earthquakes, as indicated by the locations of areas of older, uplifted, and abandoned alluvial fan surfaces. Although variatio ns 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 sl ip as large as 1 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 occurre d locally within the surficial sediments. The long-wavelength (kilometer-sc ale) variations in surficial slip may be influenced by fault geometry and p erhaps by the thickness of unconsolidated sediments. The slip variations ov er shorter length scales (tens of meters) may be caused by variations in th e proportion of the total shear that occurs on visible, brittle fractures v ersus that which occurs as distributed shear, warping or rotation. The vari ability of slip along the ruptures associated with the Landers earthquake c alls for caution in interpreting geomorphic offsets along prehistoric fault ruptures.