March 12, 2011
The data-consolidating institutional consortium IRIS–the Incorporated Research Institutions for Seismology–has a spectacular resource to visualize actual seismic waves propagating around the Earth, that everyone should check out.
Here is an animation they put together (they do this for every significant quake) displaying ground motion at recording stations set up around the U.S. You can see the dramatic passage of the seismic waves from the 8.9 quake, and you get glimpses of the waves that have circled the Earth from the other side and are passing back through heading back towards the epicenter. This is a visualization of actual recorded data–note the scale bar on the seismogram at the bottom: nearly a centimeter of ground motion all across the U.S.!
The data are from the “USArray,” a travelling deployment of seismometers meant not to detect earthquakes but to probe the interior of the Earth using seismic waves, like a giant ultrasound. Of course the array thoroughly detects earthquakes, but its density is overkill for the location and characterization of individual seismic events–that’s why it doesn’t matter that it’s migrating across the country.
Obviously right now the array predominantly occupies the great plains and is just entering the midwest. In this animation the amplitude of vertical motion is colored on a red-blue scale and the direction of motion at any given station is indicated in real time (well, sped up) as a little line directed outward from the station. It’s a pretty good way to visualize 3D ground motion if I do say so myself. The seismogram visible on the bottom is a representative one chosen near the center of the array (highlighted in yellow on the map). Those of you in the midwest–look how much was going on beneath your feet yesterday!
I highly encourage you to explore this site and the vast collection of Ground Motion Visualizations (GMVs) they have. Pick your favorite earthquake and watch it ripple through the U.S.!