3500 TERMINAL AVE Geotech Report 2022-10-25

Port of Everett—South Terminal Wharf& Electrical Upgrades— Phase 2 15 found in the new and historical explorations,which typically indicate water levels ranging from approximately 5 to 20 feet below the ground surface (MLLW elevations of+12.5 to-2.5 feet). Based on these readings, we adopted a design groundwater depth of 5 feet(elevation of approximately+12.5 feet) in our analyses.The design groundwater depth we considered represents the high water level observed and expected at the site. Table 2 - Monitoring Well Measurements Well No. Date Latitude Longitude GW Elevation (ft) 1 8/17/2016 47.974185 -122.228496 3.6 1 12/8/2016 47.974185 -122.228496 10.2 2 8/17/2016 47.974458 -122.22809 5.0 GeoEngineers has created a project-specific soil and groundwater management plan that describes the anticipated groundwater management requirements for the south terminal site in greater detail. SEISMIC DESIGN RECOMMENDATIONS Western Washington sits at the contact between two large crustal tectonic plates.The Juan de Fuca plate forms the floor of the Pacific Ocean off the coast of the northwestern United States, and moves northeastward from its spreading ridge boundary with the Pacific plate at an average rate of about 1.5 inches per year.As it converges with continental North America,the Juan de Fuca dips below(or "subducts") beneath the North American plate,forming a shallow, eastward-dipping contact interface. This boundary is known as the Cascadia Subduction Zone (CSZ), and is responsible for the seismicity in the Western Washington region, producing earthquakes associated with three types of source zones: subduction interface, subduction intraslab, and crustal (Figure 7). Subduction Interface Sources.As mentioned above, the Juan de Fuca plate moves toward North America at a rate about 1.5 inches per year, on average. However,this displacement does not manifest as slip between the two plates; rather, it is absorbed by compression of the North American plate at the interface at relatively shallow depths.This compression, based on geologic and historical evidence, is released every 500-600 years in the form of magnitude-8 to-9 earthquakes,the last such event occurring in 1700. Characteristics of this type of earthquake may include very large ground accelerations, shaking durations in excess of two minutes, and particularly strong long-period ground motions. Subduction Intraslab Sources.A deeper zone of seismicity is associated with a steeper bending of the Juan de Fuca plate, and the breaking of the plate under its own weight below the Puget Sound region.This region,termed the Benioff Zone, produces intraslab earthquakes at depths of 40 to 70 kilometers. Such past events in Western Washington include the 1949 Puget Sound, 1965 Olympia, and 2001 Nisqually ITI 19232-01 HARTCROWSL-R December 6,2017