Hi Lowell. The quake near Los Altos appears to be on the Monte Vista fault. Some say it's a reverse fault others say it's a thrust fault. According to Mal Johnston at USGS this fault showed movement during the 1989 Loma Prieta quake.

Four years ago, a group of consulting geologists funded by the USGS concluded that the Monte Vista and its sister faults have been warping an area of 60 square miles from Los Gatos to Los Altos Hills -- knocking creek beds out of plumb, heaving up bumps in the ground and opening springs. Together, the signs suggested that the fault network is active and could generate an earthquake of magnitude 6.5 to 7.

Although there is some evidence that an 1865 earthquake may have occurred on the foothills faults, scientists say they're still not sure whether these faults can produce quakes of their own or move only in response to shaking on nearby faults, as they did in 1989.

If the Monte Vista did rupture in a magnitude 6.7 quake, most of the South Bay would shake violently and the area right around the fault would shake even harder, Perkins said. She estimates that 15,000 homes and apartments would be red-tagged as uninhabitable, including 13,500 in Santa Clara County.

ABAG's scenario for the Monte Vista quake does not show, in detail, which streets or neighborhoods would shake hardest. That was deliberate, Perkins said, because scientists still don't know closer than about half a mile exactly where the faults lie. Take Care...Don in creepy town