It's been a few months since I've actually had some time to create a blog entry. This past week has been a crazy one as far as current world events are concerned. The 8.9 magnitude earthquake in Japan has devastated the Japanese people. Even though Japan is accustomed to living with strong earthquakes, this one still managed to be very destructive, despite all of the advances in structural engineering and other adaptive measures.
I have found that many people have questions about if this could ever happen here in the United States. Sadly, the answer is "Yes." and I'm not referring to the inevitable "Big One" of California's future either. Let's discuss two other "danger areas" of the U.S. that are not as well known:
The Pacific Northwest - Washington & Oregon :
About 300 miles west of the coastline lies a subduction trench (pictured below). This same type of fault is what lies on the ocean floor east of Japan that was responsible for the recent earthquake. All five of the strongest recorded earthquakes occurred as a result of a subduction trench
Subduction trenches are also responsible for volcano formation, thus explaining the volcanoes in Cascadia such as Mt. St. Helens. Unfortunately, this particular type of fault tends to create the most destructive earthquakes.
Source: Geist, Eric L., 1996. Relationship between the present-day stress field and plate boundary forces in the Pacific Northwest, Geophysical Research Letters, v. 23, p. 3381-3384. Via USGS website.
More can be found about the earthquake risk in the Pacific Northwest (Cascadia) from this website from the United States Geological Survey (USGS): http://walrus.wr.usgs.gov/earthquakes/stress/implications.html
The New Madrid Seismicity Zone:
This area of the U.S. is in the middle of the North American plate, so it shouldn't have earthquakes, right? One would be inclined to think that, but they would be sadly mistaken. The area of SE Missouri, W. Kentucky, W. Tennessee & NE Arkansas sits upon the most seismic area east of the Rocky Mountains. This area is what we could call a "sleeping giant". But why?
The last major earthquake swarm occurred in 1811-1812. Despite the limited population in the area of the time, the effects were felt for hundreds of miles. These quakes are estimated to have been around the 6.5 magnitude range, based upon information taken from the historical accounts from the events. If a quake of this magnitude were to occur today, cities like Memphis and St. Louis would suffer damage similar to that of Japan, but without the tsunami (of course).
This area lies upon an ancient network of faults that was created about 500 million years ago. This network, called the Reelfoot Rift was stretched during this time, causing some of the bedrock to sink a few inches in places. Now, 500 million years later, this same area is being squeezed, courtesy of plate tetonics. This squeezing is reactivating the fault network, thus resulting in earthquakes in this otherwise stable continental area. As you can tell from this map, this area is high risk.
Here is an overall map of earthquake risk for the U.S. Do you live in one of the high risk areas?
I hope you enjoyed this little lesson in geology. Even when there's no significant weather, there's always something in our natural world that we can talk about. Have a great week everyone and enjoy the spring-like weather!
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