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Subsurface F�p(ormion, Gealogic Nazard, and <br />Be(vedcre Lots Eart Preliminarv Geotechnical Engineering Report <br />E} crerr 15'asNin tan Geologic Hazards and Mitigarions <br />II. GEOI,OGIC HAZARDS AND MITIGATIONS <br />The following discussion of potential geologic hazards is based on the geologic, slope, and <br />shallow ground water conditious as observed and discussed herein. <br />5.0 SGISMIC HAZARDS AND RECOMMENDED MITIGATIONS <br />Earthquakes occur in the Puget Lowland with great regularity. Thc vast majority of these <br />events are small and are usually not felt by people. However. large earthqnakes do occur as <br />evidenced by the 1949, 7.2-magni[ude event, the ?001, 6.8-magnitude event, and the 1965, <br />G.5-magnitude event. The 1949 carthquake appears to have been the largest in this region <br />during recorded history and was centered in the Olympia area. Evaluation of earthquak�� <br />retum rates indicates that an earthquake of the magnitude between 5.5 and 6.0 is likely within <br />a given 20-year period. <br />Generally, there are four types of potential geologic hazards associated with large seismic <br />events: 1) surficial ground rupture; 2) seismically induced landslides; 3) liquefaction; and 4) <br />ground motion. The potential for each of these hazards [o adversely impact the proposed <br />project is discussed below. <br />5.1 Surficial Ground Rupturc <br />'fhe nearest known fault trace to the project site is the South VVhidbey Island-Lake Alice Fault. <br />located approximately 7 miles to the southwest. No surficial faulting or earth ruptwe <br />associa�ed with the South Whidbey Island-Lake Alice Fault has been documented to date in Ihe <br />Snohomish Count}� region. No ground rupture mitigalions are required. <br />5.2 Seisn��callv In�uced Landslides <br />The risk of dam�ge to the proposed structures hy seismically induced landsliding is low, <br />provided thc recommendations contained in this report are properly followed. Landslide <br />hazards are further discussed in �he Landslide Hnzurds and Mirigatio�:s section of this report. <br />5.3 Liquefaction <br />7'he encountered stratigraphy has a loa potential for liquefaction due to the density/consistency <br />of the nati��c sediments and the lack of adeerse gmund water conditions. No mitigation of <br />liyuefaction h�zards is N�arranted. <br />— --- --- --- <br />.il.n, ,, � • �� - —. . _ 455'tr('/.dTE(� E�RTH SCIC.�'CES. L�'C. <br />,n�,.: n:���. �,� r,.,,<<,,:�.:�u,i.r nr u:n Pa�c 5 <br />