Tectonic Plates Thought Responsible for Swarm of Yellowstone National Park Earthquakes

January 26, 2010

A graphic of the Yellowstone caldera. Smith and Siegel.

The recent swarm of earthquakes noted at Yellowstone National Park were most likely caused by shifts in tectonic plates, not pressures in the magma chamber beneath the park, according to geologists.

According to the Yellowstone Volcano Observatory, University of Utah semismograph stations in the park noted a pair of earthquakes Sunday evening that measured magnitudes of 3.0 and 3.1. The first event of magnitude 3.0 occurred at 11:09 p.m. and was followed by a magnitude 3.1 event at 11:21 p.m., the observatory reported.

Both shocks were located around 9 miles southeast of West Yellowstone, Montana, and about 10 miles northwest of Old Faithful. Typically, events of this magnitude are felt in and around the park, but there were no reports of these particular events being felt, the observatory noted.

These two earthquakes are part of an ongoing swarm in Yellowstone that began January 17, 2010. The largest earthquake in the swarm as of 9 a.m. MST, January 25, was a magnitude 3.8, the observatory reported. There have been 1,271 located earthquakes in the swarm of magnitude 0.5 to 3.8. This includes 11 events of magnitude larger than 3, with 97 events of magnitude 2 to 3, and 1,163 events of magnitude less than 2. There have been multiple personal reports of ground shaking from observers inside the park and in surrounding areas for some of the larger events.

Earthquake swarms are relatively common in Yellowstone.

The swarm events are likely the result of slip on pre-existing faults and are called tectonic earthquakes and are not thought to be caused by underground movement of magma, the observatory staff noted. Currently, there is no indication of premonitory volcanic or hydrothermal activity, but ongoing observations and analyses will continue to evaluate these different sources.

Seismic information on the earthquake can be viewed at the University of Utah Seismograph Stations: http://www.seis.utah.edu/.

Seismograph recordings from stations of the Yellowstone seismograph network can be viewed online at: http://quake.utah.edu/helicorder/yell_webi.htm.

Anyone who has felt earthquakes in the swarm are encouraged to fill out a form on the USGS Community Felt reports web site: http://earthquake.usgs.gov/eqcenter/dyfi/.

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