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this approach, a poisson distribution model was used to calculate the probability of occurrence of various magnitude earthquakes along the Bear Mountains and Melones faults in a 100-year period. The results of this analysis confirmed that the probability of having the MCE along these faults in a 100-year period is low. Furthermore, the analysis indicates that the preferred MPE for these faults is a magnitude 5.7 earthquake. This MPE estimate in consistent with the maximum historic earthquake (magnitude 5.7, Oroville Earthquake) associated with a northern segment of Sierran Foothills fault system. Ground accelerations resulting from earthquakes may be estimated from widely accepted, published relationships that relate ground shaking to earthquake magnitude and distance from the causative fault or earth- quake epicenter. For the San Joaquin County Landfill Development site, relationships developed by Seed and Schnabel and published in Seed and Idriss (1982) were used to estimate the level of mean peak horizontal ground accelerations that may occur at the site due to MPEs occurring in the area. Because the MPE for the Bear Mountains fault zone and the Melones fault zone are the same, and the Bear Mountains zone is nearest the site (see Plate C-1) , ground accelerations at the site for the MPE on the Bear Mountains fault zone will be greater than for the Melones fault zone. Design mean peak horizontal ground accelerations (0. 10g) , therefore, will result from the MPE (magni- tude 5.7) on the Bear Mountains fault zone, which has been mapped 28 km east of the site.