<br />15 <br /> <br />certerra.com 4660 Main Street, Suite 100, Springfield, Oregon 97478 T: 541.393.6340 <br />2.4 Seismicity <br /> <br />In accordance with Section 20.3 of ASCE 7 -22, the Site Class was determined by estimating an equivalent <br />average shear wave velocity for the upper 100 feet of the site profile (Vs) using the available subsurface data , <br />consistent with Section 20.3 guidance. The Site Class was evaluated using Vs, as well as adjusted values of Vs/1.3 <br />and Vs*1.3 to account for uncertainty in the estimated shear wave velocity. In accordance with ASCE 7 -22 Section <br />20.3, the governing Site Class is taken as the more conservative classification resulting from this evaluation. <br />Seismic design parameters were evaluated for each applicable Site Class using the ASCE 7 -22 Seismic Design <br />Map Tool, and the governing (most conservative) values were selected. Because Site Class D produced the <br />highest values of SMS, SM1, SDS, and SD1, Site Class D governs for design. Accordingly, the site coefficients <br />corresponding to Site Class D were used to develop the seismic design parameters presented below. <br /> <br />Seismic design parameters were obtained using the USGS / ASCE 7 -22 Seismic Design Map Tool <br />(https://ascehazardtool.org/) for the project location for Risk Category II and Site Class D. The ASCE 7-22 seismic <br />design parameters are presented in Table 1 below. <br /> <br />Table 1: Seismic Design Parameter Recommendations (ASCE 7-22). <br />PARAMETER ASCE 7-22 <br />Site Class D <br />Ss 0.82g <br />S1 0.37g <br />SMS 1.1g <br />SM1 0.8g <br />SDS 0.74g <br />SD1 0.53g <br />PGAM 0.49g <br />Design PGA (= PGAM /1.5) 0.327g <br />Note: Site Latitude = 44.030159°, Site Longitude = -123.05598° <br /> <br />In accordance with Section 1803.5.11 of the 2022 OSSC, we have included the following evaluation of potential <br />geologic and seismic hazards including slope instability, liquefaction, and surface rupture due to faulting or lateral <br />spreading: <br /> <br />Slope Stability <br /> <br />In our professional opinion, the risk of slope instability of the native soils on the project site is low, based on the <br />strength and consistency of the native soil strata encountered in our subsurface explorations. In addition, on the <br />date of our site investigation, most of the slopes on the project site were not overly steep (i.e. greater than 2H:1V <br />or 25 degrees from horizontal). As mentioned above, we did observe an area of the site that we consider steeply