City of Irvine
2020 Local Hazard Mitigation Plan
Figure 3-9: Seismic Hazards: Fault Rupture
large earthquakes. In this area of the City, the soils are predominantly sandy alluvial soils, and the depth to groundwater in some areas is as shallow as 10 feet beneath the ground surface. 83 Seismic shaking The intensity of seismic shaking occurs in relation to the amount of energy discharged by the seismic event, which is dictated by the length and depth of the fault. The longer and nearer the surface, the fault rupture is, the greater the seismic shaking. In most cases, areas that are nearest to the fault rupture experience the greatest seismic shaking while areas that are more distant experience less shaking. Seismic shaking can damage or destroy structures leading to partial or even total collapse. The shaking of the ground can also damage or destroy underground utilities or pipelines, potentially leading to releases of hazardous materials as well as flooding if water lines are breached. Southern California, including Irvine, is a highly seismic area as a result of the major faults that run through the region and is subject to experiencing seismic shaking. The intensity of seismic shaking is usually measured with the Modified Mercalli Intensity (MMI) scale, which is based on the amount of observed
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