INVESTIGATION OF NEARFIELD POSTSEISMIC SLIP FOLLOWING THE M(W) 7.3 LANDERS EARTHQUAKE SEQUENCE OF 28 JUNE 1992, CALIFORNIA

Repeated precise surveys of six nearfield trilateration arrays reveal that minor horizontal displacements occurred across the several fault ruptures in the five months following the Landers earthquake sequence. The displacements range from 0 +/- 2 mm on the Camp Rock and Emerson faults, to 3 +/- 2 mm on the Landers fault, to 9 +/- 2 mm on the Johns on Valley fault, to 40 +/- 5 mm on the Eureka Peak fault, consistent i n magnitude and duration with GPS and creepmeter measurements by other investigators. The relative lack of afterslip at all sites except acr oss the Eureka Peak fault is probably due to the lack of a thick alluv ial cover. Concomitant precise resurveys of level lines across the San Andreas fault in Coachella Valley and of a trilateration array at Dur mid Hill, south easternmost San Andreas fault, failed to reveal vertic al or horizontal displacements greater than the allowable uncertainty (< 1 mm for leveling; 2 mm +/- 2 ppm for trilateration). Therefore the Landers earthquake sequence did not perturb the San Andreas in any wa y that was evident from our measurements of near-surface strain.