Ground Motion Visualizations (GMVs) show how seismic waves travel away from an earthquake location by animating the motion of the ground as detected on seismometers. Each dot shown in the GMV animation is a seismic station. When the ground moves up the dot turns red, and when the ground moves down the dot turns blue.
Waves generated by an earthquake travel around and through the earth, but they get smaller, or attenuate, as they move away from the earthquake location, just like ripples in a pond.
Once the earthquake waves are far enough away from the location where the earthquake occurred, they can no longer be felt by people, but they can still be detected by sensitive seismic instruments.
The GMV shows the earthquake waves traveling both through the earth and across earth’s surface.The earthquake waves follow a Great Circle Path, which is the shortest distance between two points on a sphere.
The green triangle in the video is the reference station recording the seismogram shown along the bottom (Note the scale in micrometers/microns. For context, the diameter of a human hair is ~50-75 microns). The red line is the “great circle path” between the reference seismometer and the earthquake location (yellow star).
You can find and view GMV videos here.
Frequently Asked Questions
Q. Why does it look like some of the instruments experience shaking before the seismic waves arrive?
A. This effect is due to the setting of the animation and the calibration of the seismic instrument.
Q. Is this video in real-time speed?
A. The video is not reflecting the actual speed of the waves; it has been sped up. The time is shown along the bottom.
Q. Why are there many areas that don’t appear to have any seismic instruments?
A. If you look carefully, you will see that there are Canadian stations, primarily along the western coast and adjacent to Alaska. Not every seismic instrument in the US, Canada, or Mexico can be used in this type of animation. Certain areas, like the west coast of the US, are more heavily monitored and have more seismic stations than other regions.