6807 EVERGREEN WAY 2016-01-01 MF Import

GEOTECHNICAL ENGINEERING STUpY JMD Architecture April 19, 1999 Seismic Design Considerations E-8689 Page 7 The Puget Lowland is classified as a Seismic Zone 3 in the 1997 Uniform Building Code (UBC►. Earthquakes occur in the Puget Lowland with regularity; however, the majority of these events are of such low magnitude they are not felt without instruments. Large earthquakes do occur, as indicated by the 1949, 7.2 magnitude earthquake in the Olympia area and the 1965, 6.5 magnitude earthquake in the Midway area. There are three potential geologic hazards associated with a strong motion seismic �vent at this site: ground rupture, liquefaction, and ground motion response. Ground Rupture The strongest earthquakes in the Puget Lowland are widespread, subcrustal events, ranging in depth from thirty (30) to fifty-five (55) miles. Surface faulting from these deep events has not been documented to date. Therefore, it is our opir�ion 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 results 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 silt); it must be loose; it must be below the croundwater table; and it must be subject to sufficient magnitude and duration of groundshaking. The effects of liquefaction may be large total andlor differential settlement for structures founded in the liquefying soils. In our opinion, the potential for liquefaction induced settlement of the medium dense to very dense silty sand with gravel encountered at this site should be negligible. Eerth Con�uhann, Inc.