Oregon Coast Overdue for 'The Big One'

13-year Cascadia study complete – and earthquake risk looms large

...“Over the past 10,000 years, there have been 19 earthquakes that extended along most of the margin, stretching from southern Vancouver Island to the Oregon-California border,” Goldfinger noted. “These would typically be of a magnitude from about 8.7 to 9.2 – really huge earthquakes.

“We’ve also determined that there have been 22 additional earthquakes that involved just the southern end of the fault,” he added. “We are assuming that these are slightly smaller – more like 8.0 – but not necessarily. They were still very large earthquakes that if they happened today could have a devastating impact.”

The clock is ticking on when a major earthquake will next strike, said Jay Patton, an OSU doctoral student who is a co-author on the study.

“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,” Patton said. “The interval between earthquakes ranges from a few decades to thousands of years. But we already have exceeded about three-fourths of them.

”The last mega-earthquake to strike the Pacific Northwest occurred on Jan. 26, 1700. Researchers know this, Goldfinger said, because written records in Japan document how an ensuing tsunami destroyed that year’s rice crop stored in warehouses...

We tend to think in terms of California, from San Francisco to Los Angeles in terms of the worst threat due to earthquakes because of our cultural memory of the San Francisco earthquake of 1911, and the repeated, recent historical, though generally smaller quakes in the Los Angeles region, but the northern end of the system  from San Francisco up through Canada is a truly a time bomb.  The Cascadia fracture zone is known to produce massive, earthquakes, and being just off shore, has to likelihood of producing devastating tsunami far beyond the region of intense shaking.