Editing Seattle Fault (section)

== Hazard ==
[[File:Port-au-Prince harbour crane after 2010 earthquake.jpg|thumb|Shipping-container crane at [[Port-au-Prince]] (Haiti) harbor leaning after earthquake-induced ground failure. Seattle's waterfront faces similar risk]]
<!--  This needs to be bigger than thumbnail, else it has negligible impact. -->

The Seattle Fault (and the related Tacoma Fault) is not the only source of earthquake hazard in the Puget Lowland.  Other faults in the near surface continental crust, such as the [[Puget Sound faults#SWIF|South Whidbey Island Fault]] (near Everett), and the yet to be studied [[Puget Sound faults#OS|Olympia Fault]] (near Olympia), though historically quiescent, are suspected of generating earthquakes of around magnitude 7.  Others, such as the [[2001 Nisqually earthquake]], originate about {{convert|50|to|60|km|abbr=in}} below Puget Sound in the [[Wadati–Benioff zone|Benioff zone]] of the subducting [[Juan de Fuca plate]]; being so deep their energy is dissipated.  And there are the infrequent but very powerful great subduction events, such as the magnitude 9 [[1700 Cascadia earthquake]], where the entire [[Cascadia subduction zone]], from [[Cape Mendocino]] to [[Vancouver Island]], slips.<ref>{{Harvnb|Bucknam|others|1992}}, p.&nbsp;1611;  {{Harvnb|Fisher|others|2005}}, p.&nbsp;8.</ref>

But the Seattle and Tacoma faults are probably the most serious earthquake threat to the populous Seattle–Tacoma area.  A 2002 study of bridge vulnerability estimated that a magnitude 7 earthquake on the Seattle Fault would damage approximately 80 bridges in the Seattle–Tacoma area,<ref>{{Harvnb|Ballantyne|others|2002}}, p.9.</ref> whereas a magnitude 9 subduction event would damage only around 87 bridges in all of Western Washington.<ref>The much greater energy of subduction earthquake is spread out over a larger area, and concentrated mainly on the coast, where there is less development.</ref> The same study also found that with failure of just six bridges (the minimum damage for a Benioff M 6.5 event) there could be at least $3&nbsp;billion lost in business revenue alone.<ref>{{Harvnb|Ballantyne|others|2002}}, p.11.</ref> Subsequent retrofitting by the [[Washington Department of Transportation]] and the City of Seattle would likely reduce damage to key bridges. But there is concern that such an earthquake on the Seattle Fault would devastate [[Unreinforced masonry building|unreinforced masonry (URM) buildings]], of which the City of Seattle is estimated to have around a thousand, concentrated in [[Capitol Hill, Seattle|Capitol Hill]], [[Pioneer Square, Seattle|Pioneer Square]], and the [[Chinatown–International District, Seattle|International District]].<ref>{{Harvnb|Swanson|Findlay|2007}}, "Executive Summary", §&nbsp;2.1.3, and figure 2.</ref>

[[File:Seattle - Earthquake damage to Cadillac Hotel 2nd Ave S in Pioneer Square, 2001.jpg|left|thumb|upright|Damage to a masonry building (Cadillac Hotel) in Seattle, from the [[2001 Nisqually earthquake]]]]
Other recent work<ref>{{Harvnb|Kelsey|others|2008}}, p. 1596.</ref> indicates that the Seattle Fault can generate two types of earthquakes; both pose "considerable hazard" to the Seattle metropolitan region.  The A.D. 900–930 earthquake is believed to be the only instance in the past 7,000 years of the type that causes a regional uplift.  The other type is more localized and shallower (and therefore more damaging); at least four such events are believed to have occurred in the past 3,000 years on the west end of the fault. (The history of the central and eastern segments is not known.)

Calculations based on fault length and [[paleoseismological]] studies show that the Seattle Fault can generate a very damaging magnitude 7.0 earthquake.<ref>{{Harvnb|Bucknam|others|1992}}, p. 1613.</ref> In addition to extensive damage to unreinforced structures and structures built on fill (such as much of Seattle's Pioneer Square area, the industrial area, and the waterfront), computer modeling has shown that such earthquakes could cause a tsunami of about {{convert|2|m|abbr=in}} high on [[Elliott Bay]].<ref>{{Harvnb|Koshimura|Mofjeld|2001}}, p. 872.</ref> The modeling shows that such a tsunami would also inundate the industrial areas on [[Commencement Bay]] 30&nbsp;miles south (Tacoma) and low-lying areas on the Puyallup River delta.<ref>{{Harvnb|Walsh|others|2009}}.</ref> There is also concern that a severe or prolonged event could cause failure of the [[Duwamish River|Duwamish]] or [[Puyallup River]] deltas, where the main port facilities for Seattle and Tacoma are located (Harbor Island and Commencement Bay).<ref>{{Harvnb|Gonzalez|others|2003}}, §&nbsp;3; {{Harvnb|Kayen|Barnhardt|2007}}.</ref>
{{clear}}