shipping-container crane @ port-au-prince (haiti) harbor leaning after earthquake-induced ground failure. seattle s waterfront faces similar risk
the seattle fault (and related tacoma fault) not source of earthquake hazard in puget lowland. other faults in near surface continental crust, such south whidbey island fault (near everett), , yet studied olympia fault (near olympia), though historically quiescent, suspected of generating earthquakes of around magnitude 7. others, such 2001 nisqually earthquake, originate 50 60 km (31 37 miles) below puget sound in benioff zone of subducting juan de fuca plate; being deep energy dissipated. , there infrequent powerful great subduction events, such magnitude 9 1700 cascadia earthquake, entire cascadia subduction zone, cape mendocino vancouver island, slips.
but seattle , tacoma faults serious earthquake threat populous seattle–tacoma area. 2002 study of bridge vulnerability estimated magnitude 7 earthquake on seattle fault damage approximately 80 bridges in seattle–tacoma area, whereas magnitude 9 subduction event damage around 87 bridges in of western washington. same study found failure of 6 bridges (the minimum damage benioff m 6.5 event) there @ least $3 billion lost in business revenue alone. subsequent retrofitting washington department of transportation , city of seattle reduce damage key bridges. there concern such earthquake on seattle fault devastate unreinforced masonry (urm) buildings, of city of seattle estimated have around thousand, concentrated in capitol hill, pioneer square, , international district.
damage masonry building (cadillac hotel) in seattle, 2001 nisqually earthquake
other recent work indicates seattle fault can generate 2 types of earthquakes; both pose considerable hazard seattle metropolitan region. a.d. 900–930 earthquake believed instance in past 7,000 years of type causes regional uplift. other type more localized , shallower (and therefore more damaging); @ least 4 such events believed have occurred in past 3,000 years on west end of fault. (the history of central , eastern segments not known.)
calculations based on fault length , paleoseismological studies show seattle fault can generate damaging magnitude 7.0 earthquake. in addition extensive damage unreinforced structures , structures built on fill (such of seattle s pioneer square area, industrial area, , waterfront), computer modeling has shown such earthquakes cause tsunami of 2 m (6 feet 7 inches) high on elliott bay. modeling shows such tsunami inundate industrial areas on commencement bay 30 miles south (tacoma) , low-lying areas on puyallup river delta. there concern severe or prolonged event cause failure of duwamish or puyallup river deltas, main port facilities seattle , tacoma located (harbor island , commencement bay).
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