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Many folks (and their kids) asked why earthquakes happen in the central and eastern U.S., far away from plate boundaries. There are many reasons! #QuakeQuestions🧵
First, the plate boundary is a lot wider than you might think. In California, most motion between the Pacific and North America plates happens on the San Andreas fault. But that plate motion is stretching the crust (and causing earthquakes) as far east as the Colorado Plateau.
In the past, the tectonic plates were very different than they are today. Remnants of ancient plates and past mountain building have left faults throughout the U.S. on which earthquakes can occur to relieve stress. And there are plenty of non-tectonic stress sources. 
Ok Oregon, you asked so we’re answering your #QuakeQuestions from Monday. If you’re not already following @OregonOEM or @PNSN1 be sure to do so as they are your go-to's for local info about emergencies and earthquakes in Oregon and the Pacific Northwest.
What’s the deal with earthquakes in Oregon? As many of you mentioned in Monday's #QuakeQuestions post, this region of the U.S. is capable of hosting very large (M9!) earthquakes along the #Cascadia subduction zone where the Pacific plate slides beneath the North American plate.
How do we know such large earthquakes are possible? Check out this thread to learn more about the 1700 M9 Cascadia earthquake – the largest known earthquake to have occurred in the conterminous U.S.
