Scenario Liquefaction Hazard Maps of Santa Clara Valley, Northern California

Abstract

Maps showing the probability of surface manifestations of liquefaction in the northern Santa Clara Valley were prepared with liquefaction probability curves. These curves were based on complementary cumulative frequency distributions of the liquefaction potential index (LPI) for surficial geologic units in the study area. LPI values were computed with extensive cone penetration test soundings. Maps were developed for three earthquake scenarios, an M 7.8 event on the San Andreas fault comparable to the 1906 event, an M 6.7 event on the Hayward fault comparable to the 1868 event, and an M 6.9 event on the Calaveras fault. Ground motions were esti- mated with the Boore and Atkinson (2008) attenuation relation. Liquefaction is pre- dicted for all three events in young Holocene levee deposits along the major creeks. Liquefaction probabilities are highest for the M 7.8 earthquake, ranging from 0.33 to 0.37 if a 1.5 m deep water table is assumed, and from 0.10 to 0.14, if a 5 m deep water table is assumed. Liquefaction probabilities of the other surficial geologic units are less than 0.05. Probabilities for the scenario earthquakes are generally consistent with observations during historical earthquakes.