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Eugene City Hall R32.19.04 Rev. B. September 9, 2003 <br /> <br /> Given these issues, it is possible to establish a probabilistic level of ground shaking <br /> that might be expected to occur in or near Eugene, for various return periods. For the <br /> common return periods for a shallow soil over rock site in Eugene, the following <br /> ground motions are established: <br /> <br /> Once every 475 years: 0.14 g or more <br /> <br /> o Once every 975 years: 0.20 g or more <br /> <br /> o Once every 2,475 years: 0.30 g or more <br /> <br />Figure 4-1 shows a complete seismic hazard curve for Eugene. For new designs to the <br />1997 Edition of the UBC, the design PGA is 0.3g. It should be noted that while the <br />design PGA of 0.3g reflects a return period longer than 475 years, a dominant source of <br />the hazard is the potential for a moderately distant M 8.5 to 9 earthquake; this large <br />magnitude earthquake would cause a longer duration of ground shaking (more than 60 <br />seconds) than more common crustal events in California, and probably more damage to <br />many types of ductile structures. Table 4-1 provides the digitized values in Figure 4-1. <br /> <br /> l <br /> ': <br /> <br /> o O(~OOi <br /> <br /> o ooo0~ol _ <br /> <br /> O0 05 10 t 5 2B 25 <br /> Peak Ground Accea~ra~c:n - O <br /> <br /> Figure 4-1. Seismic Hazard Curve for Eugene <br /> <br /> Frequency of Occurrence per Year PGA (g) <br /> 5.39E-02 0.005 <br /> 4.58E-02 0.007 <br /> 3.71E-02 0.0098 <br /> 2.81E-02 0.0137 <br /> 1.98E-02 0.0192 <br /> 1.32E-02 0.0269 <br /> 8.62E-03 0.0376 <br /> 5.84E-03 0.0527 <br /> 4.20E-03 0.0738 <br /> <br /> G&E Engineering Systems Inc. Page 25 <br /> <br /> <br />