What was the biggest earthquake in Oregon?

Oregon’s Earthquake Reality: It’s Not Just California That Shakes!

Okay, so when you think of earthquakes, Oregon probably isn’t the first place that springs to mind. California, maybe, or even Alaska. But Oregon? Yep, the Beaver State has its own earthquake story to tell, and it’s one we really need to pay attention to. While we may not have the same frequency of tremors as our neighbors, the potential for a major earthquake here is very real.

Now, trying to nail down the “biggest” earthquake in Oregon is a bit tricky. What does “biggest” even mean? Magnitude? Damage? But a couple of events definitely stand out.

First up, there’s the 1873 earthquake. This one is often called the largest recorded earthquake to actually happen within Oregon’s borders. It struck way back in November of 1873, down near the California line on the coast. Experts figure it was around a 6.75 magnitude quake. Can you imagine the shaking? Reports at the time talked about damage along the coast and inland in Josephine and Jackson Counties.

But here’s the thing: that 1873 quake, as significant as it was, is just a blip compared to the sleeping giant offshore: the Cascadia Subduction Zone (CSZ). This thing is a 700-mile-long fault line stretching from Northern California all the way up to British Columbia. And it’s capable of unleashing “the big one”—a megathrust earthquake with a magnitude of 9.0 or even higher! Seriously, a game changer.

The last time the CSZ really let loose was way back on January 26, 1700. I know, ancient history, right? But that earthquake was a monster, clocking in at a magnitude 9.0. The resulting tsunami didn’t just slosh around the Pacific Northwest; it actually reached Japan! And get this: geologists tell us these massive quakes tend to happen every 300 to 600 years. We’re getting closer and closer to that upper bound…

Of course, there have been other notable shakers in Oregon’s history. Remember the Scotts Mills earthquake in 1993? That one was “only” a 5.6, but it still caused plenty of damage within a 25-mile radius of Scotts Mills, not too far from Portland. I remember that one; it was a real wake-up call that we’re not immune to earthquakes here. And let’s not forget the Klamath Falls earthquakes, also in 1993, with magnitudes of 5.9 and 6.0. Plus, even earthquakes centered elsewhere, like the 1949 Olympia, Washington quake (magnitude 7.1), have rattled Oregon, especially Portland.

So, what about the future? Well, this is where it gets a little scary. Geologists estimate there’s a 7% to 15% chance of a magnitude 9.0+ earthquake hitting the Cascadia Subduction Zone in the next 50 years. Think about that for a second. And there’s a nearly 40% chance of a magnitude 8.0 to 9.0 earthquake striking near Southern Oregon and Northern California in that same time frame.

A CSZ earthquake would be absolutely devastating for Oregon. We’re talking intense ground shaking that could last for minutes, followed by a massive tsunami with waves potentially topping 30 feet. Cities like Portland would face widespread infrastructure damage. The economic hit to Oregon? Projected to be over $32 billion. It’s a sobering thought, to say the least.

The bottom line is this: Oregon’s earthquake risk is real. The 1873 earthquake reminds us that we’re vulnerable to smaller, crustal earthquakes. But the potential for a magnitude 9.0 Cascadia Subduction Zone event demands that we take preparedness seriously. Knowing the risks and taking action is the best way to protect ourselves, our families, and our communities when the ground starts to shake. It’s not a matter of if, but when.