7425 HARDESON RD BASE FILE 2016-01-01 MF Import

� � �� GEOTECHNICAL ENGINEERING STUDY Trace and Associates July 19: 2005 Seismic Design Considerations E-11880 Page 10 Earthquakes occur in the Puget Lowland with regularity; however, the majority of these � events are of such low magnitude they are not felt withou� instruments. Large earthquakes do occur, as indicated by the 1949, 7.2 magnitude earthquake in the � Olympia area and the 1965, 6.5 magniiude earthquake in the Midway area and the 2001, 6.8 magnituda earthquake in the Nisqually area. � � � � � � � � � � � � � There are 3 potential geologic hazards associated with a strong motion seismic event at this site: ground rupture, liquefaction, and ground motion response. Ground Rupture The strongest eartliquakes in the Puget Lowland are widespread, subcrustal events, ranging in depth from 30 to 55 miles. Surface faulting from these deep events has not been documented to date. Therefore, it is our opinion that the risk of ground rupture at this site during a strong motion seismic event is negligible. Liquefaction Liquefaction is a phenomenon in which soils lose all shear strength for short periods of time during an earthquake. Groundshaking of sufficient duration resuits in the loss of grain-to-grain contact and rapid increase in pore water pressure, causing the soil to behave as a fluid. To have a potential for liquefaction, a soil must be cohesionless with a grain size distribution of a specified range (generally sand and siltl; it must be loose; it must be below the groundwater table; and it must be subject to sufficient magnitude and duration of groundshaking. The effects of liquefaction may be large total and/or differential settlement tor structures founded in the liquefying soils. In our opinion, the potential for widespread liquefaction-induced settlement at this site is negligible. This conclusion is based the generally medium dense condition of the site soils at depth, and the presence of only localized zones of light seepage. Ground Motion Response Tl�e 2003 /nternational Building Code (IBC) regulations contain a static force procedure and a dynarnic force procedure for design-base shear calculations. Based on the encountered soil conditions, it is our opinion Site Class D, Stiff Soi/ Profile, as defined in Table 1615.1.1 sliould be used to characterize the site soils. Eanh Consut�anis, Inc.