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Administrative Draft Environmental Impact Report Gill Medical Center Project Table 4.9-1.California Fault Activity Rating System Fault Activity Rating Geologic Period of Last Rupture Time Interval(years) Active(A) Holocene Within last 11,000 years Potentially Active(PA) Quaternary 11,000 to 1.6 million years Inactive(1) Pre-Quaternary Greater than 1.6 million years Source: California Geological Survey. The Interactive Fault Map provided by the USGS identifies potential seismic sources within 24 miles of the Project site.Two of the closest known faults classified as active by the California Geological Survey are the Foothills Fault, located approximately 24 miles to the east, and the Antioch Fault, located approximately 27 miles to the west.The nearest Alquist-Priolo Fault Zone (see Regulatory Setting), the Greenville Fault, is located approximately 29 miles to the southwest of the site. 4.9.1.3 Seismicity The amount of energy available to a fault is determined by considering the slip-rate of the fault, its area (fault length multiplied by down-dip width), maximum magnitude, and the rigidity of the displaced rocks. These factors are combined to calculate the moment (energy) release on a fault.The total seismic energy release for a fault source is sometimes partitioned between two different recurrence models, the characteristic and truncated Gutenberg-Richter (G-R) magnitude frequency distributions.These models incorporate our knowledge of the range of magnitudes and relative frequency of different magnitudes for a particular fault.The partition of moment and the weights for multiple models are given in the following summary. Earthquakes are generally expressed in terms of intensity and magnitude. Intensity is based on the observed effects of ground shaking on people, buildings, and natural features. By comparison, magnitude is based on the amplitude of the earthquake waves recorded on instruments,which have a common calibration. The Richter scale, a logarithmic scale ranging from 0.1 to 9.0,with 9.0 being the strongest, measures the magnitude of an earthquake relative to ground shaking. According to the California Geological Survey's Probabilistic Seismic Hazard Assessment Program, San Joaquin County is considered to be within an area that is predicted to have a 10 percent probability that a seismic event would produce horizontal ground shaking of 10 to 20 percent within a 50-year period. This level of ground shaking correlates to a Modified Mercalli intensity of V to VII, light to strong.As a result of these factors the California Geologic Survey (CGS) has defined the entire county as a seismic hazard zone. The Uniform Building Code places all of California in the zone of greatest earthquake severity because recent studies indicate high potential for severe ground shaking. Geology and Soils 4.9-2 October 2021