New liquefaction hazard maps of Santa Clara Valley, Northern California

New hazard maps for communities from San Jose to Palo Alto in NorthernCalifornia delineate the probability of earthquake-induced liquefaction,based on three scenarios: a magnitude 7.8 on the San Andreas Faultcomparable to the 1906 event, a magnitude 6.7 on the Hayward Faultcomparable to the 1868 event, and a magnitude 6.9 on the CalavarasCalaveras Fault. The probability of liquefaction is highest atapproximately 33 to 37 percent in some areas along major creeks for the SanAndreas Fault scenario when the water table is relatively shallow,according to the report published by the February issue of the Bulletin ofthe Seismological Society of America (BSSA).

Until now, scientists have offered only qualitative maps of theliquefaction hazard in the Santa Clara Valley. Liquefaction is a physicalprocess that takes place during some earthquakes, causing loose soil to actlike water rather than a solid. The liquefied sand or soil may flow and theground may move and crack, causing damage to surface structures andunderground utilities, as it did in the valley during both the 1868 and1906 earthquakes.

These probabilistic maps detail the degree of hazard within broader hazardzones and thereby provide a perspective on the actual risk to the user.

Source: Seismological Society of America