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4.Environmental Analysis Seismic Hazards The proposed project site could experience the effects of a major earthquake from one of the active or potentially active faults located in proximity to the project site. The four major hazards — associated with earthquakes are fault surface rupture(ground displacement),ground shaking, ground failure, and settlement. This EIR considers the potential for hazards associated with ground shaking,earthquake-induced slope failure(landslides), liquefaction and settlement but does not further discuss surface fault rupture. Surface fault rupture is not discussed because no active faults capable of generating surface rupture are located beneath the proposed project site. Seismic Ground Shaking Earthquakes in the San Francisco Bay and San Joaquin Valley Region could produce strong — ground shaking in the project area. Ground-shaking intensity is related to the size(i.e., magnitude)of an earthquake, the distance to the site, and the response of the geologic materials that underlie the site. As a rule, the greater the earthquake magnitude and the closer the fault — rupture to the site,the greater the intensity of ground shaking. Violent shaking is generally expected at and near the epicenter of a large earthquake, although studies of recent earthquakes, such as those conducted after the 1992 Landers earthquake, indicate that directional ground — motion along a fault can cause strong ground shaking farther away from the epicenter. Seismic hazards due to ground shaking can cause the greatest amounts of damage to structures and utilities and unsecured equipment. In 1999,California Geological Survey completed the Seismic Shaking Hazard Maps for California to describe the statewide distribution of estimated ground motion through the state. — These maps provide a conservative estimate, through probabilistic analysis, of the peak ground acceleration for all regions of California. Based on estimates of this seismic hazards assessment, peak ground acceleration in the region of the proposed project site could reach or exceed 0.3 to 0.4g(CGS, 2003a).6.,7 Seismic ground shaking is discussed further in the Impacts and Mitigation section of this chapter. 6 A probabilistic seismic hazard map shows the hazard from earthquakes that geologists and seismologists agree could occur.It is"probabilistic in the sense that the analysis takes into consideration the uncertainties in the size and location of earthquakes and the resulting ground motions that can affect a particular site.The maps are typically expressed in terms of probability of exceeding a certain ground motion.For example,the 10 percent probability of exceedance in 50 years maps depicts an annual probability of 1 in 475 of being exceeded each year.This level of ground shaking has been used for designing buildings in high seismic areas.The maps for 10 percent probability of exceedance in 50 years show ground motions that geologists and seismologists do not think will be exceeded in the next 50 years.In fact,there is a 90 percent chance that these ground motions will not be exceeded.This probability level allows engineers to design buildings for larger ground motions that geologists and seismologists think will occur during a 50-year interval,which makes buildings safer than if there were only designed for the ground motions that are expected to occur in the next 50 years.Seismic shaking maps are prepared using consensus information on historical earthquakes and faults.These levels of ground shaking are used primarily for formulating building codes and for designing buildings.The maps can also be used for estimating potential economic losses and preparing for emergency response(Peterson et al., 1999). 7 The damage level represents the estimated overall level of damage that will occur for various MMI levels.The _ damage,however,will not be uniform.Some buildings will experience substantially more damage than this overall level,and others will experience substantially less damage.Not all buildings perform identically in an earthquake.The age,material,type,methal of construction,size,and shape of a building all affect its performance(ABAG, 1998). RMC Pacific Vernalis Quarry Mining and Reclamation Project 4.7-10 ESA 1203015 Draft Environmental Impact Report May 2006