Clark County Today takes a look back at the likelihood of a major rip of the full Cascadia Subduction Zone that would trigger a magnitude 9.0 earthquake in the next 50 years
John Ley
for Clark County Today
The Great ShakeOut earthquake drill will take place on Thursday (Oct. 17) at 10:17 a.m. This is the time when the first shake is simulated, and participants should drop, cover, and hold on for at least 60 seconds. But locally, what are the odds of a major earthquake?
“Oregon is pretty boring,” says Harold Tobin, director of the PNW Seismic Network. He shared a video highlighting 40 years of earthquakes at the 2019 Pacific Northwest Earthquake Forum. Tobin noted most of the earthquakes have been in California, Washington, or offshore.
The biggest concern is a major rip of the full Cascadia Subduction Zone triggering a magnitude 9.0 earthquake in the range of 10-14 percent in the next 50 years. Put another way, there is an 86 to 90 percent chance an M9 earthquake will NOT happen in the next 50 years.
This is also relevant in the current Interstate Bridge Replacement Program (IBR) discussion for replacing the current two bridge structures. People should know the IRB is NOT designing the replacement bridge to the highest standard, which would best withstand an M9 or greater earthquake. They have previously reported they are not designing it to the 2,500-year standard; but a 500-year standard, which is the most commonly used standard for assessing seismic risk.
Read the following article Clark County Today published three years ago, regarding earthquakes here in the Pacific Northwest, as part of this year’s “Great Shakeout” event.
An additional article is about Oregon’s plans addressing seismic vulnerabilities to their transportation system.
Also read:
- Nighttime work on I-5 between Ridgefield and Woodland will replace damaged concrete panels Sept. 14-19
Granite Construction will close right and center lanes nightly on I-5 between mileposts 9.5 and 21.5 through Sept. 19. - County seeks volunteers to serve on the Bicycle and Pedestrian Advisory Committee
Clark County seeks two volunteers, including one youth member, for its Bicycle and Pedestrian Advisory Committee; deadline is Oct. 11, 2026. - Washington Rep. John Ley warns ballooning bridge budget needs reality check
Rep. John Ley says the IBR ballooned from a $44M contract to a $13B–$15B project, with phase one still $2.2B short. - POLL: The IBR project is described as only 30% designed and 30% funded after more than six years of work. How confident are you in the current management of the IBR program?
IBR’s cost has climbed from $3.2–$4.8B to $15.2B while the project remains 30% designed and 30% funded. - Opinion: Two bridges, one expanding bill
Bracchi traces how the IBR’s estimated cost grew from roughly $3B to $14.4B as Vancouver’s Bridge Shelter adds millions in annual operating costs alongside existing homelessness programs.
