Watch the waves from the M7.8 Alaska earthquake roll across seismic stations in North America! #AlaskaEarthquake (THREAD)

This animation, called a Ground Motion Visualization (GMV), shows the motion of the ground as detected on seismometers across North America - each dot is a seismic station and when the ground moves up it turns red and when it moves down it turns blue.

Waves generated by an earthquake travel around and through the earth, but they get smaller (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.

That's what this animation is showing - the waves from the M7.8 earthquake traveling both through the earth and across earth's surface - in the continental US the earthquake the waves are much too small to feel but not too small to measure.

The scale is along the bottom. It is in micrometers (microns). For reference, the diameter of a human hair is ~50-75 microns.

The star shows the location of the earthquake. The green triangle is the station recording the seismogram shown along the bottom. The red line between the 2 is the "great circle path".

*Some of the instruments look like they are experiencing shaking before the seismic waves arrive. This is due to the setting of the animation and the calibration of the seismic instrument.

**The video is not reflecting the actual speed of the waves; the actual wave speed is slower. The time is shown along the bottom.

This GMV is generated using the vertical component of our Ground Motion Visualization (GMV). To produce a better coverage, the video is based on all available stations from any FDSN data center, using the fedcatalog service ( http://service.iris.edu/irisws/fedcatalog/1/).

To see more GMV's visits http://ds.iris.edu/spud/gmv/17971022