SU0002453 - Laserfiche WebLink

Home Browse Search

Seismicity As with most of the San Joaquin Valley, the proposed project site is located in an area prone to seismically-induced groundshaking. However, this part of California is considered to be an area of rela- tively low seismicity in a state which is characterized by moderate-to- high seismic activity. During the formation of the Coast Ranges and the Sierra Nevada Mountains, numerous faults and shear zones developed. These faults are primarily in the Sierra foothills and the Coast Ranges; however, a few extend beneath the valley sediments. No active faults are known to reach the surface within San Joaquin County. Several faults beneath the valley that displace "basement" rocks, and some of the overlying sediments, are known from subsurface oil and gas exploration. The nearest of these buried faults is the Tracy-Stockton fault, approximately 4 miles north- east of the project site. The Midland fault is located approximately 25 miles east of the project site. These two faults are considered poten- tially active on the basis of earthquakes whose epicenters lay near these fault traces. However, neither of these faults is located near the site, and there is no evidence to suggest that either fault is likely to cause surface displacement in the project site area. The major faults which have historically produced earthquakes of greatest magnitude in Central California are the Calaveras, Hayward, and San Andreas faults in the Coast Ranges; the Greenville and Midland faults on the west site of the Great Valley; and the Sierra Nevada and Owens Valley faults east of the Sierra Nevada. While any of these faults could produce a sizeable earthquake during the lifetime of the project and could result in groundshaking at the project site, their distance from the site significantly reduces the severity of groundshaking and other earthquake-induced hazards such as liquefaction. The potential for liquefaction at the project site is low (San Joaquin County 1978) . The Tracy-Stockton fault does not appear to be active because subsurface data indicate that no appreciable movement has occurred for five million years or more. However, there is evidence of activity near the easternmost subsurface positions of the fault near Linden. It is not 3-46 10I-44.R3 4/10/89