More information about the Landers earthquake is available from the Southern California Earthquake Data Center. The interferogram shows that the deformation extended well beyond the immediate area of the surface rupture. The radar energy received by the satellite contains two important types of information. The image is a portrayal of the surface that resembles a conventional photograph in some ways, but not entirely. Think of the difference between a conventional photo and an infrared image, which shows warm areas as bright irrespective of their brightness in visible light.
Radar images differ from conventional photos in a similar way.
The second type of information contained in the return radar signal has to do with the round trip distance from the satellite to the ground and back again. We can think of a radar pulse as an invisible tape measure calibrated in units of the radar wavelength. We call the fractional part of the round trip distance the phase of the return signal. If we were able to acquire two radar images at different times from exactly the same vantage point in space and compare them, any movement of the ground surface toward or away from the satellite would show up as a phase difference between the images. It isn't possible to steer a satellite accurately enough to return it to exactly the same point in space on different orbits, but it's relatively easy to get within a few hundred feet and then do the necessary geometric corrections.