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Mater Dei High School October 20, 2023 Proposed Dance Studio, Santa Ana, California Project No. 3204.I 3204-I-01R (10/23) 6 4.2.3 Potential for Ground Rupture There are no known active faults crossing or projecting through the site. The site is not located in an Alquist-Priolo Earthquake Fault Zone. Therefore, ground rupture due to faulting is considered unlikely at this site. 4.2.4 Liquefaction and Dynamic Settlement Soil liquefaction is a phenomenon in which saturated cohesionless soils undergo a temporary loss of strength during severe ground shaking and acquire a degree of mobility sufficient to permit ground deformation. In extreme cases, the soil particles can become suspended in groundwater, resulting in the soil deposit becoming mobile and fluid-like. Liquefaction is generally considered to occur primarily in loose to medium dense deposits of saturated soils. Thus, three conditions are required for liquefaction to occur: (1) a cohesionless soil of loose to medium density; (2) a saturated condition; and (3) rapid large strain, cyclic loading, normally provided by earthquake motions. The site is located within an area mapped as having a potential for soil liquefaction, as defined by the Seismic Hazards Mapping Act (Act). As defined by the Act, characteristics of the site require investigation for the potential hazard and, if a hazard exists, that its effects be mitigated. Specifically, the site is mapped within the Seismic Hazards Zone, Newport Beach Quadrangle. The California Building Code and Special Publication 117A (CGS, 2008) requires that the ground motion used for this evaluation be based on a peak ground acceleration computed using the mapped ground acceleration (PGA) from ASCE 7-16 and a site coefficient (FPGA) based on Site Class, or a site specific response spectra. In accordance with the 2022 CBC, we considered a ground acceleration of 0.60g for a magnitude 6.7 earthquake (mean deaggregated) for our analyses. The potential for liquefaction was evaluated using the methods presented by the 2008 Idriss and Boulanger methodology (Idriss and Boulanger, 2008) and modifications provided in Special Publication 117A (CGS, 2008). Based on the results of our analysis, the potential for liquefaction induced seismic settlement to adversely impact the project is considered to be high. Layers of soil between the depths of approximately 10 to 32½ feet exhibit a potential for liquefaction. In general, the potentially liquefiable layers consist of loose to medium dense silty sands and clayey sands. Total seismic settlement is estimated to be on the order of 2 inches. Differential seismic settlement across a span of 40 feet is estimated to be on the order of 1-inch. The 2022 CBC and ASCE 7-16 requires that a site, determined by analysis to be vulnerable to potential collapse or failure due to soil liquefaction, be classified as Site Class F unless the proposed structure has a fundamental period of vibration equal to 0.5 seconds or less. While it is our opinion that the magnitude of liquefaction and thickness of potential liquefiable soils for this site does meet the threshold for collapse or failure, we assume that the proposed single-story buildings will have a period of less than 0.5 seconds. Therefore, Site Class D may be used, as recommended previously in this report. 1202 W Edinger Ave10/3/2024