Ask the Meteorologist: Earthquakes

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“Why don’t we get earthquakes like the other states?”

Alexis W., Hillside Elementary

Alexis asked this question quite a while ago but I decided to answer it given the recent discussion about earthquakes in the West. We all know after the past few months that even here in Oregon we can have earthquakes. The entire West Coast is along an “active continental margin” …meaning earthquakes are not uncommon. Along the East Coast the continental margin is considered “passive” which is why earthquakes are not very common there.

There are two major faults that lie along the West Coast of North America. These faults are boundaries in which plates underneath the ground, part of the Earth’s core or crust, interact with one another. The way in which they interact is coined by three phrases (dip-slip, strike-slip & convergent/divergent). These three movements describe whether plates are moving parallel and opposite from one another, horizontally toward or away from one another, or vertically away from one another.

The San Andreas Fault runs from the southern fringe of Northern California down to Southern California. There are smaller plate boundaries along this major fault and any plate movement along the San Andreas or the smaller boundaries can cause an earthquake. For Northern California up to Washington, the Cascadia Subduction Zone is what will bring earthquakes to the Northwest. The Eureka earthquake a few weeks ago was a result of a smaller boundary along the Cascadia.

The simple answer to this question is that earthquakes can certainly happen in Oregon, and large ones for that matter. Imagine a yard stick, and then picture bending this stick so that the ends are approaching one another. Eventually, if bent enough, the stick will snap. It’s a similar situation when discussing the plates underneath the ground that cause earthquakes …for the Cascadia Subduction Zone and the San Andreas Fault.

It is unknown when the next big earthquake will be but both of these major fault boundaries are overdue for a “big one” as it has been many years since the last. Unfortunately, this is not predictable and all we can do is wait and be prepared for whenever it may strike.

Meteorologist Alyssa Caroprese