7818 LARIMER RD B Geotech Report 2022-10-25

0 the stability of the proposed on -site structures provided they are properly located and designed in accordance with our recommendations given in the following paragraphs. We recommend a setback of at least 25 feet from the crest of all on -site steep slopes that are 25% or steeper. • Storm water disposal regulations of Snohomish County and City of Everette, and general drainage recommendations given in following sections should be strictly followed. • In general, areas with moderate to steep slopes present greater construction difficulties. These areas can easily become unstable as the result of poorly planned or non -engineered construction activities such as cuts and fill. Therefore, these areas should not be considered for development or disturbed without a detailed review of site grading plans and house plans by the project geotechnical engineer, and slope stability analysis and foundation design as required once the site grading plans and house plans are completed. Earthquake Related Hazards: The following paragraphs describe potential earthquake related hazards that are known to exist within most of the northwestern United States. Earthquakes in the Pacific Northwest occur due to tectonic activity associated with the subduction of the Juan de Fuca Oceanic plate beneath the North American Continental plate. The Juan de Fuca plate is converging on and thrusting beneath the North American Continental plate along the Cascadia Subduction Zone (CSZ), which is situated offshore along Washington. This convergence along the CSZ is the source of three types of earthquakes in western Washington. These are (1) deep intraplate earthquakes originating in the Juan de Fuca plate, (2) large subduction zone-interplate earthquakes that may occur along the interface between the Juan de Fuca and the North American Plates, and (3) shallow crustal earthquakes generated along faults. Most of the intraplate earthquakes have occurred within the Puget Sound region. The estimated maximum magnitudes of CSZ intraplate earthquakes are in the range of M7.0 to M7.5. Available research indicates that there is a potential for a large subduction zone earthquake near the Washington coast. To interpret earthquake potential of the CSZ plate interface, geologic lines of evidence such as coastal subsidence, stratigraphic evidence for flooding associated with earthquakes and turbidity in the ocean have been used. Based on the available geologic evidence, there is a sufficient scientific consensus to consider the CSZ plate interface as a potential earthquake source. The estimated maximum magnitudes of CSZ interplate earthquakes are in the range of M8.0 to M9.0+. The estimated recurrence interval is 350 to 500 years. Proposed Construction Project No: 0470-WA18 January 24, 2019 Page No: 4 of 17