Saticoy & Wells Community Plan & Development ... - City Of Ventura

Saticoy & Wells Community Plan and Code EIRSection 4.6 Geological HazardsLandsliding or slope instability may be caused by natural factors such as fractured or weakbedrock, heavy rainfall, erosion, earthquake activity, and fire, as well as by human alteration oftopography and water content in the soil.Table 4.6-1Significant Faults and Estimated MaximumEarthquake SizeFault NameEstimated MaximumCredible EarthquakeVentura-Pitas Point 6.9Red Mountain 7.0Oak Ridge 7.0Simi-Santa Rosa 7.0San Cayetano 7.0Arroyo Parida-More Ranch 7.2Mid Channel 6.6Santa Ynez (East) 7.1Malibu Coast 6.7Anacapa 7.5San Andreas (Mojave) 7.4Source: Cao, T, Bryant, W.A., Rowshandel, B., Branum, D., and Wills, C.(2003).The Saticoy & Wells Project Area contains no steep slopes or other earthquake-inducedlandslide areas where the previous occurrence of landslide movement, or local topographic,geological, geotechnical, and subsurface water conditions indicate a potential for permanentground displacements. Thus, landsliding is not a significant hazard within the Project Area.c. Secondary Seismic and Soil Related Hazards. Secondary seismic and soil relatedhazards include liquefaction, expansive soils, settlement, subsidence, and hydrocompaction.These types of hazards within the Project Area are discussed as follows.Liquefaction. Liquefaction is a temporary, but substantial, loss of shear strength ingranular solids, such as sand, silt, and gravel, usually occurring during or after a majorearthquake. This occurs when the seismic waves, from an earthquake of sufficient magnitudeand duration, shear a soil deposit that has a tendency to decrease in volume. If drainage cannotoccur, this reduction in soil volume will increase the pressure exerted on the water contained inthe soil. This process can transform stable granular material into a fluid-like state. Thepotential for liquefaction to occur is greatest in areas with loose, granular, low-density soil,where the water table is within the upper 40 to 50 feet of the ground surface. Liquefaction canresult in slope and/or foundation failure, and also post-liquefaction settlement. Liquefactionhazards are present in portions of the Project Area along the Brown Barranca and south of the4.6-4City of Ventura