Me: “Mom! Did you feel the earthquake?”
Mom: “You know, Maitri, I felt this couch shake and wondered what it was. But I didn’t want to say anything.”
Me: “Sweet! You felt the DC earthquake!”
Mom: “It was in Washington DC and I felt it in northeast Ohio? What magnitude?”
Me: “Good question. It was a 5.8, not very deep and those waves transmitted right through the Appalachian foreland basin and into the craton.”
Mom: “5.8 is big, right?”
Me: “Strong, shallow earthquake for that part of the world.”
Mom: “How do you know about the earthquake?”
Me: “Mom, I’m a geologist. And I’m on Twitter.”
Each family needs at least one plugged-in geologist to let the others know that they’re not crazy, they indeed experienced earthquake-related ground motion. Each family also needs a cool-as-hell parent who asks, “What magnitude?”
Callan Bentley has a great post up that includes all the details of the earthquake and is updated as more information and aftershocks come in. Not only is Callan a first-rate teacher of geology, he lives and works in the D.C. area and understands the geology of the Piedmont range and its fault system, one of which was probably reactivated causing this earthquake. He brings up an important question: “Are the aftershocks really foreshocks?” East Coast residents don’t need more anxiety what with Hurricane Irene bearing down on them, but it’s worth thinking about in terms of preparation.
This also gives me the opportunity to bring up my dislike of describing faults as discrete planes, when we should be talking about fault zones, or zones of crustal/lithospheric weakness. Before I wander off into the land of rheology and materials science, let it just suffice to say that the earth is not an isotropic, homogeneous thing at any scale and more a continuum of materials. In other words, not discrete materials in discrete layers that break or bend in ways that you would expect plastic or non-alloy metal to. To me, the North American plate is itself a collection of plates separated by zones of weakness along which land progressively sutured itself onto the craton, and where the zones of weakness themselves can span the width of the Piedmonts all the way to the whole Basin & Range. Almost the entire state of Nevada is a plate boundary in that sense.
Anyway, earthquake. And hurricane coming. Stay safe.