It is predictable as the tides: Print a story about a major earthquake striking Oregon and the chorus of skepticism begins. The latest example of this phenomenon was Tuesday's front-page story about the Oregon Department of Transportation's seismic disaster planning.
Readers can be forgiven for being skeptical of ODOT or, for that matter, a newspaper story that warns of impending disaster. But when it comes to the reality of a major quake hitting Southern Oregon, both are right.
The agency is right to plan for a disaster geologists say is not just likely but overdue. And it is right to focus on Highway 97 as the state's north-south lifeline after a "big one" hits.
The seismic behavior of what is known as the Cascadia Subduction Zone is well understood by scientists, and past quakes have been meticulously charted by examining sediment flows on the sea floor off the coast. The zone refers to the area where the edge of the Juan de Fuca tectonic plate dives beneath the continental plate. When pressures build up and are suddenly released by rapid movement, earthquakes occur.
The Pacific Northwest is known to suffer an enormous quake about every 500 years. The last one documented occurred in January 1700 — just over 300 years ago. So we're safe for another couple centuries, right?
A study by Oregon State University researchers published last year concludes that quakes centered off the Southern Oregon coast occur much more frequently — approximately every 240 years. OSU professor Chris Goldfinger, the study's lead author, says it has been longer than that since the last major quake.
"The probability for an earthquake on the southern part of the fault is more than double that of the northern end," Goldfinger says.
How likely is that? Study co-author Jay Patton:
"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."
And it will be a big one — likely 10 times more powerful than the Loma Prieta quake of 1989. That means Interstate 5, with its many bridges and elevation changes, would be impassable for a long time after a quake struck.
U.S. Highway 97 east of the Cascades and south of Highway 58 is much more likely to be repairable in the aftermath of a quake. This is not the fault of ODOT, it is simply a fact. And the agency is right to plan accordingly.
Southern Oregon residents should, too.