Glendale (PDF) - Hazard Mitigation Web Portal - State of California

Natural Hazards Mitigation PlanCity of Glendale, CaliforniaSection 6 – EarthquakesMap 6.2: Ground Shaking Zones in California(map shows areas of ground shaking with a 10 percent chance of exceedance in 50 years – the darkerzones can experience higher ground shaking because they are closer to active faults, and areunderlain by sediments that may amplify the effects of shaking)Liquefaction typically occurs within the upper 50 feet of the surface, when saturated, loose, fine- tomedium-grained soils (sand and silt) are present. Earthquake shaking suddenly increases pressure inthe water that fills the pores between soil grains, causing the soil to lose strength and behave as aliquid. This process can be observed at the beach by standing on the wet sand near the surf zone.Standing still, the sand will support your weight. However, when you tap the sand with your feet,water comes to the surface, the sand liquefies, and your feet sink.Liquefaction-related effects include loss of bearing strength, ground oscillations, lateral spreadingand flow failures or slumping. The excess water pressure is relieved by the ejection of materialupward through fissures and cracks. When soils liquefy, the structures built on them can sink, tilt,and suffer significant structural damage. Buildings and their occupants are at risk when the groundcan no longer support the buildings.2006 PAGE 6 - 9