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` , **00 <br /> Patterson Pass Business Center, Building#6 Page 6 <br /> Tracy, California <br /> Ground motion may be described in terms of the Modified Mercalli Intensity (MMI). The <br /> MMI scale is useful for categorizing the performance of structures in past earthquakes <br /> as it is based on a qualitative description of people's perceptions and the performance <br /> of different types of structures during historic earthquakes. The MMI scale and an <br /> approximate range of correlation to ground acceleration are shown in Appendix A. <br /> Fault rupture at the ground surface can cause more severe localized damage than the <br /> wide spread damage caused by ground shaking. The location of active surface faults in <br /> proximity to the site is an important factor in the earthquake hazard evaluation. Effects <br /> of ground rupture due to faulting are considered when estimating the degree of <br /> earthquake damage at existing structures located within a fault or drag zone. <br /> Soil effects that may be caused by an earthquake are seismically induced settlement, <br /> liquefaction (loss of soil strength in saturated soil deposits during strong ground <br /> shaking), and slope failure (landslides or local failures triggered by earthquakes). Loss <br /> of foundation support and excessive settlement of foundations may result from the soil <br /> related earthquake hazards, resulting in an increase in the amount of seismic-related <br /> damage a building may incur. <br /> SITE-SPECIFIC SEISMIC HAZARD <br /> Earthquake Ground Motion <br /> The site is located on the western edge of the San Joaquin Valley, which has a much <br /> lower incidence of seismic activity than does coastal California. Tracy and San Joaquin <br /> County have experienced several instances of ground shaking intensity of MMI V or <br /> greater in the past 150 years. The most intense ground shaking occurred in 1906 as a <br /> result of the San Francisco earthquake; ground shaking intensity reached MMI VI during <br /> this event. Ground shaking in Tracy typically occurs as a result of earthquakes that <br /> occur in the San Francisco Bay area to the west. Few major faults have been identified <br /> in the Tracy area, and only several potentially active faults are known to exist. The <br /> faults listed in the Table below are capable of producing moderate to strong ground <br /> shaking at the site: <br /> DISTANCE FROM RECENT MAXIMUM CREDIBLE <br /> FAULT OR FAULT ZONE SITE ACTIVITY MAGNITUDE <br /> Tracy-Stockton (potentially active 6 miles NE 5.0 <br /> Greenville 8 miles SW 1980 M5.9 7.0 <br /> Calaveras 20 miles SW 1979 M5.8 6.5 <br /> 1984 M6.2 <br /> Green Valley 39 miles NW - 7.0 <br /> Hayward 26 miles SW 1868 M7 7.1 <br /> San Andreas 45 miles SW 1906 M8.3 8+ <br /> 1989 M7.1 <br /> 05005.01 R. D. Boyens Engineering <br />