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2013 CBC SEISMIC DESIGN PARAMETERS Parameter Value Mapped Spectral Acceleration at 0.2 sec Period Ss 1.490 Mapped Spectral Acceleration at 1.0 sec Period St 0.550 Site Class --- F* Site Modified Spectral Acceleration at 0.2 sec Period MS 1.490 Site Modified Spectral Acceleration at 1.0 sec Period SM1 0.824 Design Spectral Acceleration at 0.2 sec Period SOS 1.994 Design Spectral Acceleration at 1.0 sec Period SD1 0.550 *The 2013 CBC requires that Site Class F be assigned to any profile containing soils vulnerable to potential failure or collapse under seismic loading, such as liquefiable soils. For Site Class F, the site coefficients are to be determined in accordance with Section 11.4.7 of ASCE 7-10. However, Section 20.3.1 of ASCE 7-10 indicates that for sites with structures having a fundamental period of vibration equal to or less than 0.5 seconds, the site coefficient factors (Fa and Fv) may be determined using the standard procedures. Ihe seismic desian Darameters tabulated above were calculated using the site coefficient factors for Site Class D. assuming that the fundamental Deriod of the structure is less than 0.5 seconds. However, the results of the liquefaction evaluation indicate that the subject site is underlain by potentially liquefiable soils. Therefore, if the proposed structure has a fundamental period greater than 0.5 seconds, a site specific seismic hazards analysis would be required and additional subsurface exploration would be necessary. Ground Motion Parameters For the purposes of the liquefaction analysis performed for this study, we utilized a site acceleration that is consistent with maximum considered earthquake ground motions, as required by the 2013 CBC. The peak ground acceleration (PGAM) was determined in accordance with Section 11.8.3 of ASCE 7-10. The parameter PGAM is the maximum considered earthquake geometric mean (MCE) PGA, multiplied by the appropriate site coefficient from Table 11.8-1 of ASCE 7-10. The web-based software application U.S. Seismic Design Maps (described in the previous section) was used to determine PGA, using ASCE 7-10 as the building code reference document. A portion of the program output is included as Plate E-2 in Appendix E of this report. As indicated on Plate E-2, the PGA for this site is 0.553g. Liquefaction The Seismic Hazards Map for the Tustin, California 7.5 Minute Ouadranqle, published by the California Geological Survey (CGS), indicates that the subject site is within a liquefaction hazard zone. Therefore, the scope of this investigation included a detailed liquefaction evaluation in order to determine the site-specific liquefaction potential. Liquefaction is the loss of strength in generally cohesionless, saturated soils when the pore- water pressure induced in the soil by a seismic event becomes equal to or exceeds the overburden pressure. The primary factors which influence the potential for liquefaction include groundwater table elevation, soil type and plasticity characteristics, relative density of the soil, initial confining pressure, and intensity and duration of ground shaking. The depth within which the occurrence of liquefaction may impact surface improvements is generally identified as the upper 50 feet below the existing ground surface. Liquefaction potential is greater in saturated, loose, poorly graded fine sands with a mean (cIso) grain size in the range of 0.075 to 0.2 mm (Seed and Idriss, 1971). Non-sensitive clayey (cohesive) soils which possess a plasticity index of ',i--/> SOUTHERN 'll*Illev CALIFORNIA 10 GEOTECHNICAL G&M Convenience Store #72 - Santa Ana, CA Project No. 16G123-1R Page 11