A hot spring in Yellowstone National Park. Image courtesy of the USGS.

Yesterday I left a little teaser about the current earthquake swarm going on at the Yellowstone Caldera. Eruptions readers have come through with even more information on the swarm. Over 250 earthquakes have occurred in the park over the last few days, most between 0.5-3.1 on the Richter Scale - and getting larger each day. The swarm is centered 10 miles northwest of Old Faithful, Wyoming and 9 miles southeast of West Yellowstone. However, before everyone gets too excited, Dr. Robert Smith of University of Utah (the go-to scientist when it comes to Yellowstone seismicity) seems to think this swarm is tectonically-triggered rather than magmatic. Also, he makes sure to point out that it is wholly unrelated to the Haiti earthquake of last week. Most of the quakes are 8-10 km below the surface, which is still likely above the hot magma reservoir (believed to be ~6-16 km) where hot fluids or faults lubricated by these fluids could generate seismicity. YVO has, unsurprisingly, kept the alert status at Green because these swarms are common in a "restless" caldera like Yellowstone.

Now, if you want to "hear" the seismicity of this swarm, Eruptions reader Akira Shirakawa has posted a file of the "sound" of the swarm, as he describes it:

I made a video of seismic waveforms from two monitoring stations converted into audio waveforms. It covers the first 28 hours of activity condensed in 7 minutes (that's a 240x speed up). You can hear (but also see) that activity is much more than only those reported earthquakes.

It is well worth checking out to get an idea of what exactly an earthquake swarm is - and you can follow some of the previous discussion of the data over here. As usual, when Yellowstone even shifts in its sleep, it is news!