POSTSEISMIC DEFORMATION ASSOCIATED WITH THE 1992 M-W=7.3 LANDERS-EARTHQUAKE, SOUTHERN CALIFORNIA

Following the 1992 M-w = 7.3 Landers earthquake, a linear array of 10 geodetic monuments at roughly 5-km spacing was established across the Emerson fault segment of the Landers rupture. The array trends perpend icular to the local strike of the fault segment and extends about 30 k m on either side of it. The array was surveyed by Global Positioning S ystem 0.034, 0.048, 0.381, 1.27, 1.88, 2.60, and 3.42 years after the Landers earthquake to measure both the spatial and temporal character of the postearthquake relaxation. The temporal behavior is described r oughly by a short-term (decay time 84 +/- 23 days) exponential relaxat ion superimposed upon an apparently linear trend. Because the linear t rend represents motions much more rapid than the observed preseismic m otions, we attribute that trend to a slower (decay time greater than 5 years) postseismic relaxation, the curvature of which cannot be resol ved in the short run (3.4 years) of postseismic data. About 100 mm of right-lateral displacement and 50 mm of fault-normal displacement accu mulated across the geodetic array in the 3.4-year interval covered by the postseismic surveys. Those displacements are attributed to postsei smic, right-lateral slip in the depth interval 10 to 30 km on the down ward extension of the rupture trace. The right-lateral slip amounted t o about 1 m directly beneath the geodetic array, and the fault-normal displacement is apparently primarily a consequence of the curvature of the rupture. These conclusions are based upon dislocation models fit to the observed deformation. However, no dislocation model was found w ith rms residuals as small as the expected observational error.