RADAR INTERFEROMETRIC MAPPING OF DEFORMATION IN THE YEAR AFTER THE LANDERS EARTHQUAKE

ALTHOUGH the 1992 Landers, California, earthquake sequence occurred in an area well sampled by geodetic networks(1-3), the postseismic deformation in the months following the earthquake has been measured at only 15 geodetic stations(4). Another shortcoming in the geodetic coverage occurs west of the primary rupture, where the existing geodetic observations suggest, but cannot resolve, sympathetic slip on secondary faults(1). Such measurements, which are needed to place the Landers earthquake sequence in the context of a recurring seismic cycle in California, can be obtained with the dense spatial coverage provided by satellite radar interferometry(5-9). Here we present radar maps of the surface deformation field which reveal features that would otherwise have been poorly sampled, particularly if the earthquake had occurred in a less accessible area. We see triggered slip at the level of several centimetres as far as 100 km from the primary rupture, and can resolve the geodetic signal of at least one small (magnitude similar to 5) aftershock. The amount of surface slip following the main shock is less than a decimetre, and is consistent with an exponential decay time of several months for the postseismic deformation.