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625 Cypress Avenue <br />Geotechnical Investigation <br /> <br />Project No. W1895-88-01 - 6 - April 23, 2024 <br />6.3 Site-Specific Ground Motion Hazard Analysis <br />A site-specific ground motion hazard analysis was performed in accordance with ASCE 7-16 Chapter <br />21 and Section 1613 of the 2022 CBC. <br />6.3.1 Probabilistic Seismic Hazard Analysis <br />The risk-targeted Maximum Considered Earthquake (MCER) probabilistic response spectrum consists of <br />the spectral response accelerations which are expected to achieve a 1 percent probability of collapse <br />within a 50-year period, evaluated at 5 percent damping. <br />The median spectral response accelerations having a 2 percent chance of exceedance in 50 years were <br />evaluated at 5 percent damping using the USGS PSHA hazard platform used in the National Seismic <br />Hazard Mapping Project, NSHMP-HAZ. The soil underlying the site was modeled as a Site Class “D” with <br />a corresponding average shear wave velocity (VS30) of 270 meters per second. The site class <br />determination is based on Standard Penetration Test blow count data. <br />NSHMP-HAZ uses the ground motion prediction equations (GMPEs) from the NGA-West 2 project: <br />Abrahamson-et al. (2014) NGA West 2, Boore et al. (2014) NGA West 2, Campbell-Bozorgnia (2014) NGA <br />West 2, and Chiou-Youngs (2014) NGA West 2. Each GMPE was assigned an equal weight and the <br />median value of the four GMPEs was evaluated. The median spectral accelerations were rotated to <br />maximum direction using the period specific ratios from Shahi et al. (2013 & 2014). <br />The GMPE of Campbell and Borzorgnia requires that the depth to where the shear wave velocity reaches <br />2.5 kilometers per second (Z2.5) be defined. Additionally, the GMPEs of Abrahamson-et al., Boore et al. <br />and Chiou-Youngs require that the depth to where the shear wave velocity reaches 1 kilometer per <br />second (Z1.0) be defined. The values of Z2.5 and Z1.0 were estimated using data from the Community <br />Velocity Model (CVM) Version 4 developed by Southern California Earthquake Data Center (SCEDC) <br />accessed by the OpenSHA Site Data Application (v1.5.2). <br />The MCE uniform hazard response spectrum was adjusted to risk-targeted spectral accelerations <br />corresponding to a 1 percent chance of collapse in 50 years by using the USGS Risk-Targeted Ground <br />Motion Calculator and following ASCE 7-16 Section 21.2.1.2 Method 2. <br />The risk-targeted Maximum Considered Earthquake (MCER) probabilistic response spectrum is provided <br />on Figure 6.