The Cascadia Subduction Zone is a 600 mile-long converging plate
boundary stretching from northern California to southern British Columbia. The
fault causes a major earthquake about once every 300 years. Compared to other
fault lines, this is an unusually long return time – resulting in greater
stress build-up and stronger subsequent earthquakes. The last major event (a
so-called megathrust quake) took place in 1700 and was estimated to have had a
magnitude of at least 9.0.
Since
then, the movement of the two plates has steadily built up pressure. In the
first half of the 21st century, the fault exceeds the vast majority of previous
time intervals in recorded history.* During this time, the plates finally slip,
resulting in the single most devastating earthquake in United States history.*** It is centred on the state of Oregon, with
a duration of several minutes, inflicting deadly damage to major population
centres like Portland, Seattle, Olympia and even Vancouver and Victoria. Of course,
many structures have been retrofitted and are able to withstand the earthquake,
along with the majority of newer buildings. However, years of economic trouble,
as well as a general inexperience of large earthquakes, have left many
structures vulnerable.
Bridges
and highways collapse, while the ground in the Seattle bay area liquefies,
dragging buildings underwater. Broken gas mains and power lines spark many
fires. The quake generates massive tsunamis,* which inundate coastal communities from
California to Alaska. These giant waves are sent racing across the Pacific,
causing damage as far away as Hawaii and Japan. Millions are left without
power, while emergency responders struggle to adapt to the scale of the
disaster. The death toll quickly reaches into the thousands, while the
financial cost exceeds $100 billion. Along with the similarly devastating southern California
earthquake, this disaster pushes much of the American west coast toward
financial ruin.
References
"By the year 2060, if we have not had an earthquake, we will have
exceeded 85 percent of all the known intervals of earthquake recurrence in
10,000 years." – Jay Patton
See Turbidite Event History — Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone, USGS:http://pubs.usgs.gov/pp/pp1661f/ Accessed 1st January 2013.
See Turbidite Event History — Methods and Implications for Holocene Paleoseismicity of the Cascadia Subduction Zone, USGS:http://pubs.usgs.gov/pp/pp1661f/ Accessed 1st January 2013.
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