By Ian C. Campbell Ht tip: Monica McFadden
The Conde McCullough Memorial Bridge, formerly the Coos Bay Bridge, is in the region at risk for tsunami inundation. Seismic retrofitting for Oregon's bridges is necessary to prevent infrastructure collapse in case of a megathrust earthquake from the Cascadia Subduction Zone.
But an earthquake of similar magnitude is in store for Oregon at some point, and scientists at Oregon State University have raised the warning flag again -- they predict it could be soon -- in a new report. In fact, the probability of a major quake in the next 50 years could range as high as 40 percent.
"One of the take-home messages," said Chris Goldfinger of OSU, lead author of the study, "is that these numbers are larger than people are used to seeing."
The group also studied the historic intervals between quakes over the last 10,000 years. Given that the last known major quake was in the year 1700, a quake in the next 50 years fits the pattern.
"Right now, we have already exceeded 75 percent of the known recurrence intervals over the last 10,000 years. By the year 2060, we will have exceeded 85 percent of them, if we don't have an earthquake by then," said Goldfinger. "If the Cascadia fault had a warranty against failure, it would have expired many years ago."
Although these predictions have circulated among geohazards professionals for a few years, their formal publication by the U.S. Geological Survey carries a lot of weight, said Yumei Wang of the Oregon Department of Geology and Mineral Industries. This includes being factored in to future revisions of the building code.
The Southern Oregon coast faces the greatest risk. Between Florence and Cape Mendocino, Calif., the report predicts an earthquake between 8.1 and 8.3 magnitude in the next 50 years at about 40 percent.
A larger earthquake like the 9.0 magnitude one in Japan has only a 10 percent chance, but could affect the entire Oregon coast.