Shaky ground: Faults right in our backyard

Earthquakes

Faults surround us

PORTLAND, Ore. (KOIN) – From up top looking down towards the scaling ground of Portland, you’ll notice we are definitely not flat. Faults surrounding our communities may be driving the land up or possibly hidden deep underground.

There are signs all around us pointing to these faults, according to Portland State Geologist Scott Burns.

“In nature, we are looking for straight lines. If rivers are straight or the edge of a mountain is straight, or a mountain range is sticking up and straight, a good working hypothesis is that there is a fault at the base of that,” he said.

Geologist’s say there are hundreds of faults scattered across the state of Oregon (You can interact with the local faults at this SITE), you can see if you live by one with this site here. Chances are, if you live in Portland, you are close by to a few.

“The classic one that we have here is the West Hills Fault or Portland Hills Fault. When you fly into Portland, it’s a straight light from downtown Portland to Scappoose and Rainier,” Burns said. “Why is that there? It’s a fault, and everything is uplifting along with that.”

These crustal faults are separate from what we would know as “The Big One”.

“In North America, Oregon and Washington, we have a lot of faults in the North American Plate. So all of these forces that we have are causing our rocks to have a lot of pressure. So we have stress, stress, stress, and then bam, they break,” Burns explained.

These local faults can still cause a tumble, according to Burns, because “it is a shallower earthquake with less magnitude, but it’s shallow and it will still knock us to the ground and cause liquefaction.”

However, are the faults actually active?

“Many of the faults in Oregon, [geologists] don’t know if they are active or not. To be active it has to have gone off in the last 10 thousand years. And many of them we think are active. Because everything is moving in the Pacific Northwest,” Burns said.

An earthquake of recent years that was associated with a local fault was the spring break 1993 earthquake known as the Scotts Mills earthquake that registered as a 5.6 on the Richter Scale.

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