map shows the likelihood of liquefaction Bay area
This map shows the likelihood of liquefaction in Northern Santa Clara County during a magnitude 7.8 earthquake on the northernmost segments of the San Andreas Fault.

New U.S. Geological Survey maps show, for the first time, the degree to which Northern Santa Clara Valley is at risk of liquefaction during an earthquake.

The maps draw on 10 years of research, said Tom Holzer, an engineering geologist with the USGS, and senior author of the maps. Scientists can now quantify the degree to which an area is at risk, from 0 to 40 percent.

"Earlier maps tended to use categories like high, medium and low, and never told you what 'high' meant," Holzer said Tuesday.

Liquefaction is what happens when loose, wet sand or soil is shaken by an earthquake and reacts like water rather than solid ground. This sand or soil can flow like a liquid, causing major damage to structures built atop the soil, and utilities located under this shifting ground.

Parts of the Bay Area saw liquefaction in the 1868 Hayward earthquake, as well as the 1906 San Francisco earthquake and the Loma Prieta earthquake of 1989, Holzer said.

The maps show the likelihood of liquefaction in three different earthquake scenarios: a magnitude 6.7 quake on the Hayward fault; a magnitude 6.9 quake along the Calaveras fault; and a magnitude 7.8 quake on the northern segment of the San Andreas fault, similar to the 1906 earthquake in San Francisco.

Liquefaction would be most likely in that last scenario. The USGS estimates the probability is between 33 and 37 percent along the valley's major creeks.

While this new data has a variety of uses, Holzer believes real estate developers and people buying and selling property will make frequent use of these maps.

In current state regulatory maps, "you're either in the liquefaction zone or your not," Holzer said. Now buyers can determine whether liquefaction is a serious risk for a particular property.

"Instead of black and white, it's shades of gray now," Holzer said.

The maps are available HERE.