202 ALDER ST Geotech Report 2018-01-02 MF Import

' ' ' Proposed View Ridgr Subsurface Exploration, Ceologtr Hnzards, lufiltrulion Paenn�l, Efemenrary SchW! Xepfacemenr and Preliminary Geotechnicr.l bn�ineermg Repon Evereu, tVoshington Geologi� Hazards and Miti�utioru ' 6.1 Surficial Ground Rupture ' Generally, the largest euthquakes that have occucred in the Puget Sound area are sub-crustal events with epicenters ranging from S�J to 70 kilometers in depth. Earthquakes that are generated at such depths usually do not result in fault rupture at the ground surface. However, , current research indicates that surficial ground rupture is possible in the South Whidbey Is�and � Fault Zone. The �outh Whidbey Island Fault Z�ne is not thoroughly mapped or well j , understood. We are not aware of detailed maps of active faulrs in the project area. The best , available mapping depicts multiple traces of the South Whidbey Island Fault, ail oriented ' northwe�t-southeast and passing more than 1 mile to the south of the site. We are available to ' , discuss current research related to surface faulting in the project area. I 6.2 Seismically Induced Landslides , In our pinion, the risk of seismically induced landslides at [his site is low due to the moderate inclination of site slopes and the presence of relatively dense soils at shallow depths. , 63 Liquefaction , Liquefaction is a process through which uncousolidated soil loses strengdi as a result of vibrations, such as those which occur during a seismic event. During normal conditions, the ' weight of the soil is suppurted by both grain-to-grain contacts and by the fluid pressure within the pore spaces of the soil below the water table. Exveme vibratory shaking can disrupt the graimto-grain contact, increase the pore pressure, and result in a temporary decrease in soil ' shear strength. The soil is said to be liquefied when nearly all of the weight of the soil is supported by pore pressure alone. Liquefaction can result in deformation of ehe sediment and setdement of overlying structures. Areas most susceptible to liquefaction include those areas ' underlain by non-cohesive silt and sand with low relative densities, accompanied by a shallow warer table. ' The si�e is underlain by advance outwash seJiments that are very dense and not samrated above a depth of approximately 39 feet. The liquefaction potential of the site is therefore low, in our ' opinion. We did not complete a detailed liquefaction analysis. and none is warranted, in our opinion. ' 6.4 Ground Motion Structural design of buildings should follow the current applicable building code. The ' applicable code at the time this report was written is the 2009 International Building Code QBC). The site soils are consistent with 2009 IBC Site Class "C", as defined in Tahle ' Seprember 22. 2010 ASSOCIATED FitRi N SClF.NCES. /Nt' BWG/r6 KFI(X1255A1-PrnjtntlG0ICO1551KE1WP Page 8 '