Why earthquakes travel farther in the eastern US than the West

Earthquake update

CHARLOTTE, N.C. (WBTV) - Earthquakes aren’t common in the eastern U.S. – but they can and do happen. This morning’s 5.1 magnitude earthquake southeast of Sparta woke people up… interrupted morning coffee… took out power to many in Alleghany County.

Earthquakes tend to be stronger in the West. We always hear about earthquakes in California. They are located on the western edge of the North American plate grinding along the San Andreas Fault. We’re in the middle of the North American tectonic plate. There are a few faults here but nothing like out west. There’s just not as much potential for movement.

While they tend to be stronger and there are many more of them in the western U.S., east coast earthquakes tend to be felt far and wide. Reports from this morning’s earthquake came in from all across the WBTV viewing area and from as far away as Atlanta, Pittsburgh and Cincinnati. Why would that be when there are stronger ones out west? Why aren’t they felt farther away?

It has to do with geology. Seismic waves decrease more slowly in our part of the country – so they can travel farther. Turns out, our rocks are older than they are in the west. Because they’ve been subject to extreme pressure and temperatures, they are harder and denser. Also because they are older, faults have had more time to heal. That means faults don’t stop the waves. If there was a fault, the movement from the waves wouldn’t be able to jump the break. With no break, the waves can keep on travelling. In the west, there are more faults so earthquake waves are more confined. They can travel until they get to a break/ fault and then stop or at least start to dissipate.

Over the next few days, aftershocks are possible but they aren’t likely to be as strong than the one from this morning.

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