04 ATTACHMENT 6 - Laserfiche WebLink

Project No. E9164-04-0 2 - 3 - April 15, 2020 TABLE 4.1 REGIONAL FAULT SUMMARY Fault Name Approximate Distance to Site (miles) Maximum Earthquake Magnitude, Mw Calaveras ½ 6.9 Pleasanton 2 ½ 6.6 Hayward 7 7.3 Las Positas 12 6.4 Greenville 12 6.9 Clayton 12 ½ 6.9 Silver Creek 13 ½ 6.9 Concord 14 ¼ 6.6 Contra Costa Shear Zone 17 6.5 Los Medanos -- Roe Island 19 ¼ 6.8 Faults tabulated above and many others in the Bay Area are sources of potential ground motion. However, earthquakes that might occur on other faults within the northern California area are also potential generators of significant ground motion and could cause ground shaking at the site. 4.2 Surface Fault Rupture The site is not within a currently established State of California Earthquake Fault Zone for surface fault rupture hazards. No active or potentially-active faults are known to pass directly beneath the site. Therefore, the potential for surface rupture due to faulting occurring beneath the site during the design life of the proposed development is considered low. By CGS definition, an active fault is one with surface displacement within the last 11,000 years. A potentially- active fault has demonstrated evidence of surface displacement with the past 1.6 million years. Faults that have not moved in the last 1.6 million years are typically considered inactive. 4.3 Ground Shaking We used the USGS web-based Unified Hazard Tool to estimate the peak ground acceleration (PGA) and mean and modal magnitude associated with a 2,475-year return period that corresponds to an event with 2 percent chance of exceedance in 50 years. The USGS estimated PGA is 1.3 g and the mean and modal (most probable) magnitude is 6.9 for Seismic Site Class D (Vs30 = 259 m/sec) based on a recent 2014 model within the application. While listing PGA is useful for comparison of potential effects of fault activity in a region, other considerations are important in seismic design, including frequency and duration of motion and soil conditions underlying the site. 4.4 Liquefaction The site is located within a State of California Seismic Hazard Zone for liquefaction and web-based mapping by the USGS and CGS indicates a high susceptibility to liquefaction at the site. Liquefaction is a phenomenon in