Report - PEER - University of California, Berkeley

the minimization of the negative of the natural logarithm of the likelihood function(Equation 2). The regression analysis was performed using the software JMP (SASInstitute, Inc. 1995). This analysis was performed separately for each earthquake and forselected periods. In the following sections, the details of 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/soft rock, shallow stiff soil, and intermediatedepth stiff soil, respectively) was assumed, but no significant differences were observedin the resulting attenuation relationships. Consequently, the subdivision of 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 of potentially liquefiable sand deposits (Site F) is mainly a functionof whether or not liquefaction is triggered or partially triggered (i.e., significant porepressure generation develops) at the site. Triggering of liquefaction is a function of theintensity and duration of ground motion, the relative density of the soil, the permeabilityof the soil, the fines content of the soil, as well as other factors. If liquefaction istriggered or nearly triggered, ground motion is a function of a number of parameters,including rate of excess pore pressure generation, dissipation of pore pressure, reductionof effective stress, shear modulus degradation, duration of motion, as well as other13