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4 Environmental Analysis 4.7 Geology, Soils, and Paleontological Resources Seismic Ground Shaking Ground shaking occurs due to a seismic event and can cause extensive damage to life and property and may affect areas hundreds of miles away from the earthquake's epicenter. The extent of the damage varies by event and is determined by several factors, including (but not limited to) magnitude and depth of the earthquake, distance from the epicenter, duration and intensity of the shaking, underlying soil and rock types, and integrity of structures. The San Francisco Bay Area is seismically active, and moderate to severe ground shaking in the region is possible. However, the UCERF3 model results discussed above suggest that the probability of significant ground shaking caused by an earthquake near the Project site is relatively low. Liquefaction Liquefaction occurs during strong seismic shaking in locations with unconsolidated sediments that are saturated with water. This combination of conditions and action can cause the ground to become unstable. During an earthquake, sediments under these conditions can behave like a liquid, potentially causing severe damage to overlying structures. Lateral spreading is a type of landslide that can occur when unconsolidated liquefiable materials break and spread due to the effects of gravity, usually down gentle slopes. Liquefaction-induced lateral spreading is the finite, lateral displacement of gently sloping ground due to pore-pressure buildup or liquefaction in a shallow, underlying deposit during an earthquake. This phenomenon's occurrence depends on many complex factors, including the intensity and duration of ground shaking, the particle-size distribution of the soil, its density, and shallow groundwater presence. The soil parent material in both the Project site and the gen-tie corridor is unconsolidated alluvium, and the soils are all very fine-grained (clays to clay loams)and generally very cohesive.Therefore, the potential for liquefaction is expected to be low. Landslides Landslides occur when rock, soil, and other debris are displaced by gravity. The potential for material to detach and move down slope depends on multiple factors, including the type of soils, soil moisture content, and the steepness of the terrain. The existing land surface at the Project site has rolling hills and moderate topographic relief (approximately 170 feet of elevation difference). There are no mapped landslides on or around the site or the gen-tie route (DOC 2021). Therefore, landslides in the native materials at the Project site do not normally occur. Subsidence Land subsidence is the gradual settling or sudden sinking of the earth's surface due to subsurface movement of earth materials. Compaction of subsurface water-containing geologic layers is the primary cause of land subsidence. Regional ground subsidence typically is caused by compaction of subsurface geology as a result of petroleum or groundwater withdrawal. Subsidence has been documented in some areas of the San Joaquin Valley as well as the Sacramento/San Joaquin Delta. However, there are no areas of subsidence identified in the Diablo Range, including the vicinity of the Project site and gen-tie corridor (USGS 2022). Griffith Energy Storage Project 4.7-7 Tetra Tech/SCH 2022120675 Draft Environmental Impact Report August 2023