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� SuLsnrfnce ErplorarJnrt, Geofogic Ha;ard, nnd <br /> ' Nousing Hopt Phasr 1l Prcliminnry Gcorcc�•iica!Fatginrtnng Report <br /> Errrert. Rashingron Gmfogic Ha:ards and Midgmions <br /> I ewrthquake appears to have been the largest in this area during recorded history. Evalua:ion of <br /> retum rtes indicates chat an earthquaie of the magnitude between 5.5 and 6.0 is likely within <br /> a gi��en 20-year period. <br /> � Gcnerally, there are four tyFes of ��otential geologic hazards associated with large seismic <br /> events: 1) surficial eround rupmre; 2) scismically induced landslides; 3) liquefaction; and <br /> � 4) ground motion. The po[ential f�r each of these hazards to adversely impact the proposed <br /> project is discussed below. <br /> �� 6 1 Surficial Ground Rupture <br /> � Geoerally, the lareest earthquakes thut have occuaed in the PugPt Sound area aze sub-erustal <br /> e�•en[s with epicenters ranging from 50 to 70 kilometers in depth. For this reason, no surficial <br /> fawting or earth rupmre, as a resul[ of deep, seismic acciviry has been documented, to date, in I <br /> � the area of the subject site. Therefore, it is our opiniQn, based on existing geologic data, that <br /> rhe risk of surface rupture impacting th� proposed project is low. <br /> � 6.2 Seismicallv Induced Landslides <br /> Generalized slope stahiliry h,lzards and landslide potentia( has been addressed in Section 5.0 <br /> I above. During strong seismic shakine, there is an increased potential for shallow slope ( <br /> in:,cabiliry along the w�estern margin of the propused development area. Therefore, butnessing � <br /> I the toe of the s'wpe or o[henvise retaining these slopes would significantly reduce the risk of � <br /> seismically induceci landsliding. btore detailed evaluation of these risks may be required by <br /> the regulating govemment agency once a specific retaining wall rype is chosen. i <br /> ! 6.3 Liquefaction <br /> � The encountered stratigraphy has a low potential for liquefaction due to the absence of ground <br /> water within the upper, loose, si�ry sand soils, and the high silt content and high strength of the <br /> underlying [ill. <br /> � 6.4 Ground btotion <br /> � The project site is located within a Zone 3 rating for seismic activity on a scale of 1 (lowest) to <br /> 4 (highest) based on the Seismic Zone h/op of the United S�ates, Figure No. 16-2 in the 1997 <br /> � edition of the Unijorm Building Code (UBC). This zoning is based on past earth�uake activiry <br /> in the Puget Sound region. As such, design recommendations in the report ac:.ommodate the <br /> possible effect of seismic activity in areas with a Zone 3 rating, corresponding to a peak <br /> I ground acceleration of 0.3g (a Richter magnitude 7.5 earthquake occurring directly beneath the <br /> site), in accordance with UBC guidelines, using soil type Sc. This soil type corresponds to <br /> seismic coeificients C, = 0.33 and C. = 0.45. <br /> i Fe6nrnry ll. 2002 ASSOCUTED E4RTX SCIENCE$ INC. <br /> SG1I�N-KfD1:+DA2.omjrai�:Nl J�fl'�KE1WP-ti:K �/ <br /> Page 7 <br /> I %3b <br /> \ <br />