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

Saticoy & Wells Community Plan and Code EIRSection 4.6 Geological HazardsThe U.S. Geological Survey defines active faults as those that have had surface displacementwithin Holocene time (about the last 11,000 years). Holocene surface displacement can berecognized by the existence of cliffs in alluvium, terraces, offset stream courses, fault troughsand aligned saddles, sag ponds, and the existence of steep mountain fronts. Potentially activefaults are those that have had surface displacement during Quaternary time, within the last 1.6million years. Inactive faults have not had surface displacement within the last 1.6 millionyears. A fault is a plane or surface in the earth along which failure has occurred and materialson opposite sides have moved relative to one another in response to the accumulation andrelease of stress. Faults that are known to have moved in recent history (the last 200 years) areconsidered historically active. Faults that have exhibited signs of activity during the last 11,000years are considered active, and faults that have exhibited signs of activity within 11,000 yearsto 2 to 3 million years ago are considered potentially active. Ground surface displacementalong a fault, although more limited in area than the ground shaking associated with it, canhave disastrous consequences when structures are located across or near the fault zone.Amounts of movement during an earthquake can range up to tens of feet. Fault displacementmay also occur gradually, not as a result of earthquakes, but as the nearly imperceptiblecontinual movement known as creep. Creep can produce the rupture or bending of buildings,fences, railroads, streets, pipelines, curbs, and other linear structures.Faults in the Project Area. Potentially active faults within in the Project Area include theCountry Club Fault and McGrath Fault. The Country Club Fault is a northwest-southeasttrending zone in the eastern portion of the City between Kimball Road and Wells Road to thewest and east, and Telegraph and Telephone Roads to the north and south. This fault isconsidered potentially active; however, it was evaluated in 1976 and was not designated as anAlquist-Priolo Special Studies Zone. The McGrath Fault runs along the Santa Clara River on thesouthern boundary of the Project Area. Other faults within the vicinity of the Project Areainclude the Ventura-Foothill Alquist-Priolo Zone, and Oak Ridge. Areas on or around activeand potentially active fault traces are potentially subject to surface rupture. These faults mayproduce damaging ground shaking and are shown on Figure 4.6-1.Effects of Seismicity. Table 4.6-1 shows the estimated maximum earthquake that mayoccur due to activity along the most significant faults that could affect the Saticoy & WellsProject Area. It includes active regional faults such as the San Andreas and the Anacapa thatare known to produce tremors sufficient in magnitude to affect large areas.In the event of a strong earthquake (magnitude 6.0 to 7.5) originating in southern VenturaCounty or a major earthquake (8.0 magnitude) along the San Andreas Fault, damage to manyexisting structures could be severe and some loss of life could occur.b. Landslides. A landslide is the perceptible downslope movement of earth mass. It ispart of the continuous, natural, gravity-induced movement of soil, rock and debris. Landslidingcan range from downslope creep of soil and rock material to sudden failure of entire hillsides.Landslides include rockfalls, slumps, block glides, mudslides, debris flows, and mud flows.4.6-2City of Ventura