6801 SEAWAY BLVD Geotech Report 2025-08-19

Seaway Commercial Center Subsurface Exploration,Geologic Hazard, 7007 Seaway Boulevard and Geotechnical Engineering Evaluation Everett, Washington Geologic Hazards and Mitigations II. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on the geologic, slope, and shallow groundwater conditions, as observed and discussed herein. 5.0 LANDSLIDE HAZARDS AND MITIGATION It is our opinion that the risk of damage to the proposed distribution center by landsliding is low due to the lack of steep slopes at the project site and vicinity and the presence of dense to very dense glacially consolidated soils. No detailed slope stability analysis was performed for this project, and none is warranted, in our opinion. 6.0 SEISMIC HAZARDS AND MITIGATION Earthquakes occur in the Puget Lowland relatively frequently. The vast majority of these events are small, and are usually not felt by people. However, large earthquakes do occur, as evidenced by the 1949, 7.2-magnitude event; the 2001, 6.8-magnitude event; and the 1965, 6.5-magnitude event. The 1949 earthquake appears to have been the largest in this region during recorded history and was centered in the Olympia area. Evaluation of earthquake return rates indicates that an earthquake of the magnitude between 5.5 and 6.0 is likely within a given 20-to 40-year period. Generally, there are four types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture, 2) seismically induced landslides, 3) liquefaction, and 4) ground motion. The potential for each of these hazards to adversely impact the proposed project is discussed below. 6.1 Surficial Ground Rupture Based on review of the Washington State Department of Natural Resources (WADNR) Geologic Information Portal website, suspected traces of the southeastward extension of the South Whidbey Island Fault Zone (SWIFZ) are located about 2.5 miles southwest of the site.The recognition of this fault splay is relatively new, and data pertaining to it is limited with studies still ongoing. The recurrence interval of movement along this fault system is still unknown, although it is hypothesized to be in excess of 1,000 years. Due to the long recurrence interval, the potential for surficial ground rupture is considered to be low during the expected life of the proposed development, and no mitigation efforts beyond complying with the 2018 International Building Code(IBC) are recommended. December 17,2021 ASSOCIATED EARTH SCIENCES,INC. PEL/Id-20200319E001-002 Page 6