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4.Environmental Analysis ._ Impact 4.7.4: In the event of a major earthquake,seismic ground shaking could potentially injure people and cause collapse or structural damage to proposed structures.This would be a potentially significant impact. During the life of the project, there is a potential that ground shaking from a moderate to strong earthquake would be felt at the proposed RMC Pacific Vernalis Quarry site. Ground shaking from a moderate to strong earthquake generated from an earthquake fault in the San Francisco Bay or — San Joaquin/Sacramento Regions could generate peak ground accelerations at the proposed project site that could reach 0.5 g and therefore cause damage to structures, unsecured equipment and engineered and non-engineered quarry slopes. As discussed previously in this chapter, the — potential for surface fault rupture or other secondary effects of earthquake ground shaking, such as liquefaction, are not considered a significant impact to the proposed quarry operation. The difficulty in assessing earthquake risk at the proposed RMC Pacific Vernalis Quarry is partly due to the lack of historic data regarding earthquakes that cause noticeable ground shaking and damage in the San Joaquin Valley. Simply stated, there has not been an earthquake in recent — history strong enough to cause ground shaking in the Vernalis-San Joaquin region sufficient to affect the performance of active quarry operations. The strong earthquake on the northern Hayward Fault Zone, for instance, which many experts anticipate in the next 30 years,could result in substantially more ground shaking than the Bay Area experienced during the Loma Prieta earthquake in 1989.The Loma Prieta event is the most recent moderate to strong earthquake to affect the Bay Area and to be felt in certain areas within the San Joaquin Valley region. With an epicenter located approximately 140 miles southeast of San Francisco, this event caused considerable damage to the Bay Area but caused only limited damage in the San Joaquin Valley. The Loma Prieta event is the largest earthquake to affect the Bay Area-San Joaquin Delta Region since the Great Earthquake of 1906. Some scientists believe that the Bay Area and San Joaquin Delta region are overdue for a large earthquake. The USGS has determined a 62 percent — likelihood of a strong to moderate earthquake occurring in the Bay Area in the next 30 years (USGS WG02, 2003). Such an event could cause damaging ground shaking at the project site and vicinity. — As discussed in the analysis of Impact 4.7.1, above,Geomatrix evaluated the stability of temporary and permanent slopes using a slope stability model. Typically,these models are sufficiently conservative and although not able to predict actual performance of a slope during an earthquake, they are able to provide engineers with an adequate estimation of dynamic stability. Seismologists also use other methods to estimate the ground acceleration on a particular site — using information on earthquake fault characteristics,historic seismicity, and underlying geology. Based on information provided by the Geomatrix study (Geomatrix, 2002),and by other published data(i.e.,CGS, 1991;CGS, 2000), earthquake ground shaking could originate from causative faults in the Bay Area or San Joaquin-Sacramento Valley region, including the Great Valley thrust fault, the San Joaquin fault,the Midway-Black Butte fault, the Vernalis fault,or the _ Marsh Creek-Greenville fault. At the proposed project site,the ground shaking generated by a moderate to strong earthquake _ could cause failure on temporary and permanent excavation slopes(as discussed previously) and cause some equipment damage. Specifically,equipment at the processing plant could undergo RMC Pacific Vernalis Quarry Mining and Reclamation Project 4.7-22 ESA/203015 Draft Environmental Impact Report May 2006