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35 <br /> V <br /> Historical Seismic Activity <br /> Historic earthquake data indicate the closest larger recorded earthquake was <br /> about 19 miles northeast of the site. This 1881 event was estimated to have a <br /> Richter magnitude of about 5.0, and is thought to have been along the Tracy- <br /> Stockton fault (San Joaquin County, 1978) . Such an event may have generated a <br /> peak ground acceleration of 0.03 g at the site (using Campbell (1981) uncon- <br /> strained attenuation relationship] . In 1903 a Richter magnitude 5.5 event <br /> occurred along the Calaveras Fault Zone, about 37 miles southwest of the site. <br /> This 1903 earthquake may have caused a 0.02 g ground acceleration onsite. <br /> Predicted Ground Acceleration <br /> Although the exact time and magnitude of future earthquakes is uncertain, <br /> deterministic estimates of earthquake activity can be based on the seismotectonic <br /> setting, fault length, and historical activity of the regional faults. Geolo- <br /> gists often refer to these deterministically estimated earthquakes as maximum <br /> probable and maximum credible events. A maximum probable earthquake is the <br /> maximum earthquake that is likely to occur during a 100-year interval (CDMG, <br /> 1975) . A maximum credible earthquake event is the largest earthquake that a <br /> fault is believed to be capable of generating, without regard to the recurrence <br /> interval (CDMG, 1975) . <br /> Listed below is the distance between pertinent faults and the site, and the <br /> maximum credible and maximum probable earthquakes that can be generated along <br /> these faults. Seismically induced ground acceleration at a specific area is a <br /> function of both distance between the epicenter and site and the magnitude of the <br /> earthquake. Using the seismic attenuation relationship of Campbell (1981, <br /> unconstrained) , the expected peak acceleration from both maximum probable and <br /> maximum credible earthquakes are listed below. <br /> Peak Ground Acceleration at the Site from <br /> Maximum Probable (MPE) and Maximum Credible WE Earthquakes <br /> Distance to Site Acceleration* Acceleration* <br /> Fault Name (miles) MPE (g) MCE (g) <br /> San Joaquin 5 5** 0.1 6** 0.2 <br /> Tracy-Stockton 7 5** 0.08 6** 0.13 <br /> Midland Fault Zone 20 6** 0.06 7** 0.12 <br /> Calaveras 36 6.5 0.05 7.5 0.11 <br /> Green valley-Concord 38 6.5 0.05 7 0.07 <br /> Hayward 43 7 0.06 7.5 0.09 <br /> San Andreas 60 8 0.1 8.25 0.11 <br /> •Campbell (19811 unc$nsta4ne� attQnuation relationship. �_iiMcClelland <br /> ** to es es tt mate us n m n a data. <br /> 1144A/CC-35 <br />