2401 TAYLOR DR Geotech Report 2022-10-25

2401 Taylor Drive Geotechnical Engineering Study Everett, Washington The proposed project will not impact the steep slope area and all construction will be completed behind the recommended top of steep slope setback. Based on review of the USGS Topographic Map of the Mukilteo Quadrangle(2017)the steep bluff on the west end of the subject lot is approximately 70 feet in height. We recommend a top of steep slope setback of at least 70 feet, which is at least as stringent as that required by the 2018 International Building Code (IBC) Chapter 1808.7. Seismic Hazards and Mitigations The subject property does not meet the definition in EMC Title 19, Chapter 19.37.80(A)(2) for a Seismic Hazard Area. However, earthquakes occur in the Puget Lowland with great regularity. The 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 1965, 6.5-magnitude event; and the 2001, 6.8-magnitude event. The 1949 earthquake appears to have been the largest in this area during recorded history. Evaluation of 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 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. Surficial Ground Rupture The project site is located approximately 2 miles north of the South Whidbey Island Fault Zone. This fault system has been hypothesized to have a reoccurrence interval in excess of several thousand years. Due to the suspected long recurrence interval and distance from the subject site,the potential for surficial ground rupture is considered to be low during the expected life of the proposed development. No mitigation efforts beyond complying with the requirements of the local jurisdictions and the 2015 International Building Code (IBC) are recommended for this site. Seismically Induced Landslides The potential risk of damage to the proposed structures by seismically induced land sliding is moderate due to the steeply sloping topography on the north end of the project site, in our opinion. Implementation of the recommended 80-foot top of steep slope set back will mitigate and reduce the potential risk to the property. November 6, 2019 SONDERGARRD GEOSCIENCES, PLLC 3