June 30 – Whose Fault Is It?

Today’s factismal: The Cascadia fault stretches more than 600 miles from Canada to California.

Anything you want to see in Seattle is either uphill or downhill; there are no flat parts to the city. That’s because the entire area is being squeezed together by the Juan de Fuca and North American plates. That collision has created the vast Olympic and Cascade mountain ranges (and volcanoes such as Mt. St Helens, Mt. Hood, and Mt. Rainier); the hills of Seattle are just the little foothills before the big mountains. The subduction zone also creates lots and lots of earthquakes. On average, Seattle has a magnitude 7 earthquake about once every fifty years; the last one was in 1965. Even better, the Cascadia fault is expected to create a magnitude 9 temblor every 400 years or so; the last one was in 1700.

Thnderbird figures in many of the local legends about earthquakes (My camera)

Thnderbird figures in many of the local legends about earthquakes
(My camera)

But what is the Cascadia fault? It is where the two plates meet. This 620 mile long intersection runs from Vancouver down to Cape Mendocino and stretches more than 40 miles across. Because the fault is so large and because it typically releases the stored energy all at once, it is sometimes called the “Cascadia megathrust”. Call it what you will, the amount of energy and damage that this thrust can release is simply astounding. A typical megathrust earthquake releases the same amount of energy that the USA uses in a week; put another way, it has the same power as 32,000 atomic bombs! (But it pales before a hurricane which would take just one hour to release the same amount of energy.) The last megathrust earthquake created a tsunami that raced across the Pacific Ocean and destroyed much of the island of Honshu; the temblor also created a landslide that is known in local legends as “the Bridge Of The Gods”.

The giant whale on the back fought Thunderbird and created the mountains and lakes by a series of earthquakes (My camera)

The giant whale on the back fought Thunderbird and created the mountains and lakes by a series of earthquakes
(My camera)

The amazing thing about the earthquake is that we know so much about it. And that is mainly because people talked about it when it happened and the events turned into legends that archeoseismologists could study. Today, we don’t need to wait for the legend to be born to learn about earthquakes. All you have to do is tweet! If you have a Twitter account and feel an earthquake or landslide, please send a tweet and mark it @USGSTed. To learn more, flit over to:
http://gallery.usgs.gov/audios/326#.VYg6t3JFCRs

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