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4� File No. 'A7-1909-JZ °'' November 3, 1981 foundation systems, premoisturizati n programs for soil subgrades, or f the placement of nonexpansive fill building pads, may be required for t.J this site. These mitigating measures should be determined in a final soil investigation. 4. The site could be affected by earthquakes with epicenters on any of the major faults in the Bay Area. At present, it is not possible to predict when or where movement will occur on these faults. It must be assumed, however, that movement ala g one or more of these faults will ,j result in a moderate or major earth cake during the lifetime of any construction at this site. Two major active fault systems are known to exist in the vicinity of the ite. The Greenville Fault is approximately 9 miles to the southwest, and the Calaveras Fault is approximately 25 miles to the southwest. it 5. In the event of an earthquake, seismic risk to a structure will depend on the distance of the structure from the epicenter and source fault, the character and magnitude of the earthquake, the geologic, ground Fi water and soil conditions underlyinc the structure and its immediate J vicinity, and the nature of 'the ton truction. Ground rupture (surface faulting) tends to occur along lines of previous faulting. As there is no evidence for the presence of active or potentially _ active faulting P, on the site, the potential for ground rupture is considered to be low. The potential seismic hazards at" the site are those phenomena resulting from ground vibrations generated during an earthquake. These secondary seismic 'effects consist of ground shaking and associated ground failures, such as liquefaction and associated lateral spreading, lurch cracking, and local subsidence induced by densification of liquefiable �ry soil . 6. A moderate to major earthquake on the Calaveras or San Andreas Faults, could cause severe ground shaking at this site. Structural damage due to ground shaking is caused by the transmission of earthquake vibrations from the ground into the structure. The variables which determine the extent of damage are: The characteristics of the underlying materials, the workmanship used in construction, the location and magnitude of the a rthquake, and the duration and intensity of shaking. The most dest uctive effects of an earthquake : i usually occur in areas where the gro nd is unstable and structures are inadequately designed and/or constru ted. Preliminary estimates of ground response characteristics at t is site indicate that high peak bedrock accelerations can be expected during a moderate to major =j ea-rthquake on the Greenville, Haywarl or Calaveras Fault or a major earthquake on the San Andreas Fault. The duration of the vibration waves depends upon ' the magnitude ind location of the earthquake. 14 Structures at the site should be designed to accommodate earthquake vibrations as set forth in the Uniform Building Code (2976 edition or later) . 7. If liquefaction were to occur, lateral forces induced by the earthquake motions in the soil horizons above tie zone of liquefaction, could tend to drive that layer of soil toward a y open channels. The presence of a potentially liquefiable sand layer in boring no. I and . the open L channel in the northwest corner of tie site creates a potential for 5 Applied sad Mechanics