2721 WETMORE AVE MARQUEE APARTMENTS Geotech Report 2023-06-22

Subsurface Exploration, Geologic Hazard, and 2721 Wetmore Preliminary Geotechnical Engineering Report Everett, Washington Seismic Hazards and Mitigations II. SEISMIC HAZARDS AND MITIGATIONS The following discussion of potential seismic hazards is based on the geologic and groundwater conditions as observed and discussed herein. 5.0 SEISMIC HAZARDS AND MITIGATION Earthquakes occur in the Puget Lowland with great regularity. Fortunately, the vast majority of these events are small and are usually not felt by people. However, large earthquakes do occur, as evidenced by the February 28, 2001, 6.8-magnitude event; the 1965, 6.5-magnitude event; and the 1949, 7.2-magnitude event. The 1949 earthquake appears to have been the largest in this area during recorded history and was centered in the Olympia area. Generally, there are three types of potential geologic hazards associated with large seismic events: 1) surficial ground rupture, 2) liquefaction, and 3) ground motion. The potential for each of these hazards to adversely impact the proposed project is discussed below. 5.1 Surficial Ground Rupture The nearest known fault trace to the project is the Southern Whidbey Island Fault Zone (SWIFZ) located approximately 6 miles to the south of the site. A recent study by the USGS (Sherrod et al., 2005, Holocene Fault Scarps and Shallow Magnetic Anomalies Along the Southern Whidbey Island Fault Zone near Woodinville, Washington, Open-File Report 2005-1136, March 2005) indicates that "strong" evidence of prehistoric earthquake activity has been observed along two fault strands thought to be part of the southeastward extension of the SWIFZ located about 6 to 8 miles south of the site. The study suggests as many as nine earthquake events along the SWIFZ may have occurred within the last 16,400 years. The recognition of this fault splay is relatively new, and data pertaining to it are limited with the studies still ongoing. The recurrence interval of movement along this fault system is still unknown, although it is hypothesized to be in excess of one thousand years. Due to the suspected long recurrence interval, the potential for surficial ground rupture along the SWIFZ is considered to be low during the expected life of the proposed structure and no mitigation efforts beyond complying with the 2015 International Building Code (IBC) are recommended. 5.2 Liquefaction The encountered stratigraphy has a low potential for liquefaction due to the lack of observed groundwater and the gradation and the high relative density/consistency of the natural sediments. No mitigation of liquefaction hazards is warranted. May 28,2019 ASSOCIATED EARTH SCIENCES,INC. FSM/Id 190168E001-2 Projects\20190168VKE\WP Page 6