Friday, November 22, 2013

What states are safe from earthquakes?

Where are you safe? Really nowhere. If you live in the Pacific Northwest, tornadoes are extremely rare, and hurricanes non-existent - but you are at risk of a large subduction earthquake and floods. If you live in the Southeast, you generally don't have to worry about earthquakes, but you are certainly living in Hurricane Alley. When I first took up my 5-year assignment to serve as chief scientist for volcano hazards in Vancouver, WA, in 2002, I was frequently asked the question: will we have a big eruption soon? I told everyone that I had voted with my feet, made an informed decision, and bought a house in Clark County. Two years later, of course, Mount St Helens erupted. While it briefly threatened the Johnston Ridge Observatory north of it, it was never really a threat to people in Clark County... though an ash-plume erupted on March 5, 2005 did apparently intersect an aircraft flight-path near Roseburg, WA. At least three Boeing 747 aircraft have lost all or almost all of their engines when they flew through a volcanic ash cloud. The aircraft flying over Roseburg was diverted to a nearby airport, thoroughly checked out, and found to be OK however.

Q: I saw on your website that 39 states are endanger of earthquakes, what 11 are not and why?
 Kaitlyn S, 8th grade Endeavor Charter School student

A: Hi, Kaitlyn,

If you go to this web-page you will see a map of earthquakes in the United States:

You can count 11 states that have no recent seismicity (no red circles) - but this doesn't necessarily mean they are earthquake-free. 

The longer answer to your question is that earthquakes happen where there is crustal movement: mountains rising (Hawaii and Utah, for instance), crustal slabs sliding past each other (California), or continents riding over oceanic plates (most of the West Coast). If you look at this map, you will see states that have no apparent earthquakes. This is because they are in the center of a very old, stable continental crust, and not on the tectonically active margins. However the map of RECENT seismicity could fool you into thinking that Oregon is relatively free of risk. In fact, the same subduction fault off the coast from northern California to British Columbia threatens the western sides of three American states and one Canadian province. This kind of fault may not rupture for centuries at a time. However, when it does break it will be a real attention-getter. 

One thing to keep in mind is that distance from a fault offers increasing protection: Western Washington State is at much greater risk than eastern Washington State, for instance. This is because the energy of the earthquake falls off with distance, just like sound does. Sit on the edge of your bed and have your brother kick the edge next to you. If he then goes around and kicks the other side, it will not feel nearly as uncomfortable to you. 

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