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Patterson Pass Business Center, Building#6 Page 5 Tracy, California SECTION 3: SEISMIC RISK INTRODUCTION The amount of damage to an individual building subjected to strong earthquake ground shaking will depend on a number of variables, including the intensity and duration of ground shaking, building configuration, structural systems, materials of construction, structural details including connections, non-structural components, and quality of construction. Published seismic risk evaluation methodologies for existing buildings are used as guidelines for calculating seismic damage estimates. The performance of any specific structure can, and generally will, deviate substantially from the average values given by empirical loss functions. Therefore, the estimated damage calculated using average loss functions may be increased or decreased to account for specific site and building characteristics. The seismic risk analysis methodology utilized for this evaluation includes four phases: seismic hazard evaluation, structural appraisal, determination of the mean damage estimate per published documents (ATC-13 and NCEER-95-0003), and estimation of the project-specific seismic risk. SEISMIC HAZARD EVALUATION The seismic hazard evaluation is a description of potential earthquake effects at the site and a statement of the likelihood of their occurrence. Possible effects include ground shaking, ground rupture, and soil liquefaction. Building or other improvements on the site do not influence the hazard. Faults in close proximity to the site are evaluated for their potential to produce earthquake ground shaking at the site. Earthquakes with a high probability of occurrence during the life of a building produce moderately strong ground shaking. Major earthquakes with a small probability of occurrence during the building life are capable of producing very strong ground shaking at the site. Strong ground motion for this evaluation is defined as that ground motion having a probability of exceedance of 10 percent in a 50-year exposure period, which has an average recurrence interval of 475 years. Stated differently, there is a 90 percent confidence level that ground motion at the site will not exceed the 475-year level in any 50-year period. This level of ground motion has the same exceedance probability as the seismic zone map published as part of the seismic design requirements of the Uniform Building Code. The 475-year earthquake is sometimes described as the maximum probable or design level earthquake. This method of hazard determination is consistent with the "Scenario Loss" (SL) as defined in the "Standard Guide for the Estimation of Building Damageability in Earthquakes" published by ASTM. 05005.01 R. D. Boyens Engineering