8615 7TH AVE SE Geotech Report 2018-01-02 MF Import

Subsurface Exploration, Geologic Hazard, and S.,. Mary Magdalen Sport Court Preliminary Geotechnical Engineering Report Everett Washington Geologic Hazards and Mitigations II. GEOLOGIC HAZARDS AND MITIGATIONS The following discussion of potential geologic hazards is based on the geologic, slope, and shallow ground water conditions as observed and discussed herein. 5.0 SEISMIC HAZARDS AND MITIGATION 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 tbt' 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-year period. Generally, there are four types of potential geologic 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. 5.1 Surficial Ground Rupture Generally, the largest earthquakes that have occurred in the Puget Sound area are sub -crustal events with epicenters ranging from 50 to 70 kilometers in depth. For this reason, no surficial faulting or earth rupture as a result of deep, seismic activity has been documented to date in the area of the subject site. Therefore, it is our opinion, based on existing geologic data, that the risk of surface rupture impacting the proposed project is low. 5.2 Liquefaction Liquefaction is the process of a loose, saturated sand losing its internal shear strength when subjected to cyclic loading as may happen during an earthquake. Since the project site is underlain by medium dense to dense till, the potential for liquefaction to occur is low. 5.3 Ground Motion Based on the site stratigraphy and visual reconnaissance of the site, it is our opinion that any earthquake damage to the proposed structure when founded on a suitable bearing stratum would be caused by the intensity and acceleration associated with the event and not any of the April 2 24 006 ASSOCI:ITED EARTH SCIENCES, INC. R,IP/m - KE0602MAI - PmJegs120060260LWWP Page 5