615 75TH ST SE Geotech Report 2022-10-25

Subsurface Exploration, Geologic Hazard, and Boardwalk Condominium, Building C Geotechnical Engineering Report Everett, Washington Geologic Hazards and Mitigations Fault Zone. The South Whidbey Island Fault Zone is not thoroughly mapped or well understood. We are not aware of detailed maps of active faults in the project area. The best available mapping depicts multiple traces of the South Whidbey Island Fault, all oriented northwest-southeast and passing no closer than approximately 6 miles to the southwest of the site. We are available to discuss current research related to surface faulting in the project area. No mitigation efforts beyond complying with the 2009 International Building Code (IBC) are recommended. 6.2 Seismically Induced Landslides There is a steep rockery-faced slope in the area of the proposed building foundation improvements. While it is possible that a seismically induced landslide could occur, in our opinion, the proposed construction should not increase the likelihood of a seismically induced landslide. The proposed construction is designed to support the foundation loads on deeper, denser native sediments that are less prone to landslide movement. 6.3 Liquefaction The encountered stratigraphy has a low potential for liquefaction due to the density of the native soils and lack of widespread ground water. No liquefaction mitigation efforts are recommended. 6.4 Ground Motion The guidelines presented in the 2009 IBC Section 1613 should be used in the seismic design of the project. Earthquake Ground Motions Parameters software version 5.0.9a available from the United States Geological Survey (USGS) Earthquake Hazards Program website (http://earthquake.usgs.gov/hazmaps/) using the 2009 IBC analysis option was used to determine interpolated probabilistic ground motion values in percent of gravity (g) for an event with a return period of 2 percent exceedence in 50 years. Using the software, the project area was submitted using latitude and longitude for unfactored spectral accelerations, which were determined to be Ss = 1.21 for short periods (0.2 seconds) and Si = 0.43 for a 1-second period. Based on the results of our subsurface exploration and our estimation of soil properties at depth utilizing available geologic data, Site Class "C", in conformance with Table 1613.5.2 of the IBC, may be used. September 12, 2012 ASSOCIATED EARTH SCIENCES, INC. FEW&-EE120288A8-Projects1201202881EE1 WP Page 7