SATELLITE RADAR INTERFEROMETRIC MAP OF THE COSEISMIC DEFORMATION FIELD OF THE M=6.1 EUREKA VALLEY, CALIFORNIA EARTHQUAKE OF MAY 17, 1993

Interferometric combination of pairs of synthetic aperture radar (SAR) images acquired by the ERS-1 satellite before and after the Eureka Valley, California earthquake of May 17, 1993 maps the coseismic deformation field. The fringes corresponding to contours of equal change in satellite-to-ground distance can be enhanced by forming the sum of two of such interferograms with altitudes of ambiguity roughly equal in magnitude but opposite in sign. The resulting composite interferogram reveals some 10 cm of change in range indicating a coseismic deepening of the Eureka Valley graben. After unwrapping, filtering and decimation, the range changes are used to estimate the centroid and focal mechanism. These estimates indicate normal faulting on a rupture patch compatible with the distribution of aftershocks and mapped Quaternary faults. The change in elevation produced by this earthquake resembles the current topography scaled by a factor of 20,000.