I'm guessing, but the SCEC catalogue(s) might be best for southern California and not for northern. A couple of years ago I went to the SCEC data center pages and rooted around and found Hauksson's relocated quakes...since 1930 or some such thing, and converted them to the Gocad 3D format, and looked at them in 3D. There were a bunch of quakes at precisely 6 km (or was it 5) depth...which means they were just assigned that depth. These were probably older quakes that were not relocated. I think I also got Haukkson's ~1975-2004 focal mechanisms...this catalogue tends to be almost to present. At the time, I think a couple of years (late 70s?) were missing..
Chris