In March, Elizabeth Cottrell, a geologist at the Smithsonian’s National Museum of Natural History and director of the Institution’s Global Volcanism Program, created a helpful video explanation of Japan’s devastating Sendai Earthquake. So when a magnitude 5.8 quake occurred in Mineral, Virginia, yesterday, just 84 miles southwest of Washington, D.C., we went to her with our questions.
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Why was the earthquake felt over such a broad geographic range?
The East Coast has much more contiguous bedrock that is less broken up by faults and other kinds of tectonic boundaries. On the West Coast, there are just a lot more faults, which damp the energy. On the East Coast, energy can pass more efficiently and travel farther.
What other factors play into how an earthquake is felt?
It has to do with the nature of the material you are sitting on. If you have sediment that sloshes around you can get a lot more damage or a lot more ground motion than you feel on solid ground for the same magnitude earthquake. This was also a shallow earthquake, so it went through less material.
What is known about the faults in that area of Virginia?
The USGS has a very good write-up and very nice map about this fault system and the history of the faults. It definitely is a very large earthquake, the largest we have on record, especially recorded with modern instruments, for this system. I think people on the West Coast are somewhat poking fun of the East Coast. But this earthquake is certainly nothing to sneeze at.
What do they know so far about this fault?
It’s a reverse fault, part of the Central Virginia Seismic Zone. A reverse fault is a thrust fault—one piece of rock sliding over another along a plane—with a high angle, meaning the fault goes into the earth more steeply. They are the opposite of normal faults. It is the kind of thing that is easy to diagram but difficult to explain.
What damage happened at the museum and your lab?