Waves of seismic activity from the Aug. 23rd quake in Virginia swept across the country, as shown in the video below (via)
As the blogger writes:
" ... an enormous number of sensors in the Midwest and Great Plains. These are areas not known for seismic activity, so what are they doing with so many sensors?
They are part of a travelling array (the 'transportable array') of seismometers, part of the Earthscope initative from the National Science Foundation.
The idea is to have a substantial number of seismometers moving stepwise across the US every few years. Then, having a dense array of seismometers, particularly to have them in places that we don't normally, will show us things that we don't normally see. That spectacular wave propagating across the country is one of those things. Get in to the data and you start seeing that the seismic waves didn't travel the same speed in all directions. And that tells us something about what the earth is made of. No idea what is up, but take a look at the Texas-Louisiana area. Early in the propagation of the waves, they follow along with the rest of the US. But later in the animation, that area shows much larger amplitude variations. Why?"