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Published June 1994 | Published
Journal Article Open

Spatial and temporal distribution of slip for the 1992 Landers, California, earthquake


We have determined a source rupture model for the 1992 Landers earthquake (M_W 7.2) compatible with multiple data sets, spanning a frequency range from zero to 0.5 Hz. Geodetic survey displacements, near-field and regional strong motions, broadband teleseismic waveforms, and surface offset measurements have been used explicitly to constrain both the spatial and temporal slip variations along the model fault surface. Our fault parameterization involves a variable-slip, multiple-segment, finite-fault model which treats the diverse data sets in a self-consistent manner, allowing them to be inverted both independently and in unison. The high-quality data available for the Landers earthquake provide an unprecedented opportunity for direct comparison of rupture models determined from independent data sets that sample both a wide frequency range and a diverse spatial station orientation with respect to the earthquake slip and radiation pattern. In all models, consistent features include the following: (1) similar overall dislocation patterns and amplitudes with seismic moments of 7 to 8 × 10^(26) dyne-cm (seismic potency of 2.3 to 2.7 km^3); (2) very heterogeneous, unilateral strike slip distributed over a fault length of 65 km and over a width of at least 15 km, though slip is limited to shallower regions in some areas; (3) a total rupture duration of 24 sec and an average rupture velocity of 2.7 km/sec; and (4) substantial variations of slip with depth relative to measured surface offsets. The extended rupture length and duration of the Landers earthquake also allowed imaging of the propagating rupture front with better resolution than for those of prior shorter-duration, strike-slip events. Our imaging allows visualization of the rupture evolution, including local differences in slip durations and variations in rupture velocity. Rupture velocity decreases markedly at shallow depths, as well as near regions of slip transfer from one fault segment to the next, as rupture propagates northwestward along the multiply segmented fault length. The rupture front slows as it reaches the northern limit of the Johnson Valley/Landers faults where slip is transferred to the southern Homestead Valley fault; an abrupt acceleration is apparent following the transfer. This process is repeated, and is more pronounced, as slip is again passed from the northern Homestead Valley fault to the Emerson fault. Although the largest surface offsets were observed at the northern end of the rupture, our modeling indicates that substantial rupture was also relatively shallow (less than 10 km) in this region.

Additional Information

© 1994 Seismological Society of America. Manuscript submitted 28 July 1993. We owe thanks to many for providing information and data. Jim Mori and Sue Hough helped access USGS FBA records, Dennis Ostrum and Bill Iwan helped with the SMA-2 data and response, Egill Hauksson supplied the relocated aftershock seismicity, and Jeff Freymueller, Ken Hudnut, and Mike Lisowski generously provided their surveyed and corrected (GPS and trilateration) displacements. Discussions with B. Cohee, D. Dreger, H. K. Thio, K Hauksson, D. Heimberger, K. Hudnut, K. Sieh, and H. Kanamori added significantly to this work. Reviews by S. Hartzell, B. Cohee, and C. Ammon improved this manuscript. This work was supported in part by SCEC contract through USC No. 569933 funded by NSF EAR 89-20136 and by the U.S. Geological Survey under Contract No. 1433-93-G2322 while D.J.W. was at Caltech.

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August 22, 2023
August 22, 2023