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4 Environmental Analysis 4.7 Geology, Soils, and Paleontological Resources 4.7.1.3 Geologic Hazards Seismicity The Alquist-Priolo Earthquake Fault Zoning Act (1972) and the Seismic Hazards Mapping Act (1990) require the State Geologist to delineate regulatory "Zones of Required Investigation" for active faults. It also established a standardized classification of known and mapped faults in California, by their period of activity: oo Historic faults (faults considered to be "active" faults because they have evidence of displacement within the last 200 years); oo Holocene faults (faults which have evidence of displacement greater than 200 years ago but less than 11,700 years); oo Late Quaternary faults (older faults with evidence of displacement between 11,700 years ago and 700,000 years ago); and oo Quaternary faults (oldest faults with undifferentiated age of displacement, but presumably more than 700,000 years ago). There are no known Historic or "active" faults within the Project site (CGS 2010) or gen-tie corridor. There are two faults in the area (Greenville and Las Positas) that are identified as Historic, and these are Fault Zones of Required Investigation. However, they are located more than 7 miles west of the Project site. There is one Late Quaternary fault (Midway), which actually traverses the northeast quadrant of the Project site. Finally, there are two Quaternary faults, the Black Butte Fault and the Corral Hollow Fault, located about 3 to 4 miles southwest of the Project site. Only the Greenville and Las Positas fault zones are listed as Alquist-Priolo Earthquake Fault Zones, while the Midway, Corral Hollow, and Black Butte faults, because of their age, are not. Surface Fault Rupture The Project site and gen-tie corridor do not intersect an established Alquist-Priolo Earthquake Fault Zone, as mapped by the State Geologist (Jennings et al. 2010). The nearest fault that has been designated an Earthquake Fault Zone (i.e., there is evidence of surface rupture sometime in the last 11,700 years) is the Greenville fault zone (over 5 miles west-southwest of the Project site). Although there are other mapped faults in the area (including the Midway fault which traverses the Project site), none of these faults show evidence of movement within the last 11,700 years. The U.S. Geological Survey and CGS developed a version of the Uniform California Earthquake Rupture Forecast (UCERF3) model to evaluate the likelihood of surface rupture caused by an earthquake (Field et al. 2014). The UCERF3 results are available in a Google Earth file, showing the probability of an earthquake with a magnitude of 6.7 or greater on the Richter scale for specific faults or fault zones. The model results for the Greenville fault zone suggest the probability is between 1 percent and 8 percent of such an earthquake occurring within the next 30 years. The model also provides results for the Great Valley Fault (roughly equivalent with the Black Butte fault), suggesting a probability of less than 1 percent that a magnitude 6.7 or greater will occur within the next 30 years. Therefore, the probability of surface rupture caused by an earthquake near the Project is low. Griffith Energy Storage Project 4.7-6 Tetra Tech/SCH 2022120675 Draft Environmental Impact Report August 2023