FIGURE 8.1 (Top) Deformation resulting from fault slip that occurred in the 1999 Hector Mine earthquake in the Mojave Desert, California, is revealed in this synthetic aperture radar interferogram. An interferogram is generated by taking the difference in phase of two radar images taken from the same location in orbit, but at two different times (here, September 15, 1999, and October 20, 1999). Just as the interference fringes seen on an oil slick reveal small changes in thickness of the oil film,the interference fringes shown represent small changes in distance from the satellite to the ground. (Bottom) The centimeter-level sensitivity to the surface deformation pattern permits a determination of the distribution of slip many kilometers below the surface,yielding unprecedented insight into earthquake physics. The C-band satellite used to make these observations performs adequately in desert regions; longer-wavelength L-band InSAR satellites are needed to obtain similar information in vegetated areas. In addition, because of the 5 weeks that elapsed between observations,the image of coseismic deformation is corrupted by the postseismic deformation that occurred after the earthquake (see Box 8.2). Finally, even though this is a desert region,the image is degraded by noise due to atmospheric effects that could be removed if many more observations could be stacked. SOURCE: Zebker et al., 1999. Courtesy of H.Zebker, Stanford University.