Traveling Seismic Waves
Seismic measurements recorded on August 23rd during the earthquake centered in Virginia show how the shock wave traveled across the USA. If you didn’t feel it, it was because the movements measured are very small.
What you’re seeing here are vertical displacement measurements from an array of detectors that are part of the USArray/EarthScope facility (you can read more about the array and the animation on the IRIS website). These are very sensitive instruments; note the scale on the lower graph showing the motion is only about 40 microns top-to-bottom! That’s less than the thickness of a human hair.