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The June 28, 1992, Mw 7.3 Landers earthquake occurred in the southeastern Mojave Desert, California. Over 10,000 aftershocks of the earthquake were recorded by the Caltech-USGS Southern California Seismic Network (SCSN) in 1992. To investigate the relationship between complexities in the crustal structure and variations in seismicity, we have used a tomographic method to invert 145,098 P wave arrival times from 3740 Landers earthquake aftershocks and 1148 other events recorded by 60 permanent and temporary SCSN stations. We determined a detailed P wave tomographic image with a spatial resolution of about 5 km and relocated the hypocenters with the obtained 3-D velocity model. The results show a correlation between seismicity patterns and velocity patterns and a tendency for regions rich in seismicity to be associated with higher velocities. The higher velocity areas are considered to be strong and brittle parts of the fault zone, which are apt to generate earthquakes. In contrast, low velocity areas are probably more ductile and weaker, allowing aseismic slippage.