Report - PEER - University of California, Berkeley
Report - PEER - University of California, Berkeley
Report - PEER - University of California, Berkeley
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the minimization <strong>of</strong> the negative <strong>of</strong> the natural logarithm <strong>of</strong> the likelihood function(Equation 2). The regression analysis was performed using the s<strong>of</strong>tware JMP (SASInstitute, Inc. 1995). This analysis was performed separately for each earthquake and forselected periods. In the following sections, the details <strong>of</strong> each analysis for the two eventsare described.Northridge EarthquakeThe data distribution by site type is shown in Figure 4. Initially, a separationbetween sites C 1 , C 2 and C 3 (weathered/s<strong>of</strong>t rock, shallow stiff soil, and intermediatedepth stiff soil, respectively) was assumed, but no significant differences were observedin the resulting attenuation relationships. Consequently, the subdivision <strong>of</strong> Site C wasignored in the preliminary analysis. Similarly, differences for deep soil sites based on ageand soil type (i.e., Holocene or Pleistocene and primarily cohesive or cohesionless) werealso not considered in the preliminary analysis.The response <strong>of</strong> potentially liquefiable sand deposits (Site F) is mainly a function<strong>of</strong> whether or not liquefaction is triggered or partially triggered (i.e., significant porepressure generation develops) at the site. Triggering <strong>of</strong> liquefaction is a function <strong>of</strong> theintensity and duration <strong>of</strong> ground motion, the relative density <strong>of</strong> the soil, the permeability<strong>of</strong> the soil, the fines content <strong>of</strong> the soil, as well as other factors. If liquefaction istriggered or nearly triggered, ground motion is a function <strong>of</strong> a number <strong>of</strong> parameters,including rate <strong>of</strong> excess pore pressure generation, dissipation <strong>of</strong> pore pressure, reduction<strong>of</strong> effective stress, shear modulus degradation, duration <strong>of</strong> motion, as well as other13