Recent Yellowstone earthquake swarm was the second-largest ever
Posted by JAC on 3/1/2010, 7:28 am
Posted: 02/27/2010 10:52:48 AM MST
Updated: 02/27/2010 11:11:44 AM MST


The Yellowstone earthquake swarm that began on Jan. 17 and ended on Feb. 11 was the second-largest earthquake swarm ever at Yellowstone National Park, according to scientists at the University of Utah.

During the swarm, there were 1,805 tremors of which 22 were felt by people in the park as well as adjacent communities in Montana and Idaho.

The university has more than two dozen earthquake- monitoring stations in the park.

The earthquakes were centered about 10 miles northwest of the Old Faithful area on the northwestern edge of the Yellowstone Caldera, according to the Yellowstone Volcano Observatory.

The swarm began around 1 p.m. on Jan. 17.

According to the Yellowstone Volcano Observatory, the area has had swarms over a 30-year period. The quakes did not appear to have any affect on geyser activity or cause any land upheavals.

Not only was the swarm the second-largest ever recorded at Yellowstone but it was longer in time and included more earthquakes than last year's swarm beneath Yellowstone Lake, which occurred in December 2008 and January 2009, according to the scientists.

Calculations by the University of Utah Seismology Research Group, of the total seismic energy released by the swarm corresponds to one earthquake with an approximate magnitude of 4.4

The largest swarm at Yellowstone remains the Fall 1985 swarm, which was located in the same area of the northwest corner of the Yellowstone Caldera.

The 1985 swarm produced 3,156 earthquakes during a three month period starting on Oct. 4, 1985, according to the university.

The 2010 swarm included 14 events with a magnitude larger than 3; 136 events of magnitude 2.0 to 2.9 and 1,655 events with a magnitude of slightly more than 0.0 to 1.9.

The largest earthquakes were a pair of earthquakes of magnitude 3.7 and 3.8 that occurred after 11 p.m. on Jan. 20.

Yellowstone Volcano Observatory scientists said the swarm was likely the result of slips on pre-existing faults and are not thought to be caused by the movement of underground magna or an indication of pending eruptions.

The observatory is a partnership of the United States Geological Service, the National Park Service and the University of Utah.

The swarm in 2008-2009 resulted in 813 earthquakes under the north end of Yellowstone Lake. The earthquakes had magnitudes ranging up to 3.9.

Generally, earthquakes less than a magnitude 3.0 are not felt by people. It typically takes an earthquake of magnitude 4.0 or greater to cause structural damage and a magnitude 6.5 earthquake to cause the ground to rupture.

Howard Pankratz: 303-954-1939 or hpankratz(at)denverpost.com



Read more: http://www.denverpost.com/news/ci_14483885?source=rss#ixzz0gvYkGe8I
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