* * * 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. * During this time, the plates finally slip, resulting in the single most devastating earthquake in United States history. In the first half of the 21st century, the fault exceeds the vast majority of previous time intervals in recorded history. Since then, the movement of the two plates has steadily built up pressure. 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 on the Richter scale. Compared to other fault lines, this is an unusually long return time – resulting in greater stress build-up and stronger subsequent earthquakes. The fault causes a major earthquake about once every 300 years.
The Cascadia Subduction Zone is a 600 mile-long converging plate boundary stretching from northern California to southern British Columbia. At some point during this period, the USA is struck by the most devastating earthquake in its history
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