Ground liquefaction can be a major cause of damage, injuries and deaths in earthquakes. It occurs when water-saturated sands, silts, or (sometimes) gravels are shaken so violently that the sediment loses strength. Ground cracking or lateral spreads (landslides on very shallow slopes) are common above liquefied layers. Photos from the deadly Christchurch earthquake in New Zealand show evidence of liquefaction.
Mapping areas susceptible to liquefaction can help planners and builders to better understand the potential risks of an earthquake. Following the Nisqually earthquake of 2001 near Olympia, DNR was awarded a grant by the Federal Emergency Management Agency and Washington Emergency Management Division to develop earthquake hazard maps for every county in the state.
The earthquake hazard maps (completed in 2004) show liquefaction susceptibility and areas where soils amplify ground shaking. The maps are available for state and local governments to update hazard mitigation plans and delineate geologically hazardous areas under the Growth Management Act. These large image files can be viewed or downloaded from DNR’s Division of Geology and Earth Resources.