Small Tremors Rattle National Park After Big Quake 2,000 Miles Away
Released November 04, 2002
November 4, 2002 -- A major, magnitude-7.9 earthquake that rocked Alaska on Sunday apparently triggered scores of earthquakes some 2,000 miles away at Yellowstone National Park in Wyoming.
By 8:30 a.m. MST Monday Nov. 4 - about 17 hours after the Alaskan quake - more than 200 small earthquakes had been detected occurring in clusters throughout the Yellowstone area. The quakes were recorded by the Yellowstone seismic network operated by the University of Utah Seismograph Stations.
The smallest events were of magnitude less than 0 and the largest of about magnitude 2.5. National Park Service rangers at Old Faithful and Canyon Village reported feeling some of the earthquakes.
While the data are preliminary, they suggest that the Yellowstone earthquakes may have been triggered by the passage of large seismic waves generated by the Alaskan earthquake more than 3,200 kilometers (almost 2,000 miles) from the park. The apparent triggering is suggested by the fact the Yellowstone activity began within a half hour of the Alaska earthquake, which hit at 3:12 p.m. MST Nov. 3 (1:12 p.m. local time in Alaska).
There also are preliminary reports the Alaska quake may have triggered smaller tremors at The Geysers geothermal area in northern California.
Scientists once believed that an earthquake at one location could not trigger earthquakes at distant sites. But that belief was shattered in 1992 when the magnitude-7.3 Landers earthquake in California's Mojave Desert triggered a swarm of quakes more than 800 miles away at Yellowstone, as well as other jolts near Mammoth Lakes, Calif., and Yucca Mountain, Nev.
The apparent triggering of the Yellowstone tremors by the Alaska quake "confirms what we are beginning to see worldwide - that earthquakes can be triggered by other earthquakes at great distances, more so than we had thought before," said Robert. B. Smith, a University of Utah professor of geology and geophysics and coordinating scientist for the Yellowstone Volcano Observatory.
Clusters of small earthquakes in time and space are common in Yellowstone. However, the clusters of Yellowstone earthquakes following the Alaskan mainshock extended across much of the park and were not concentrated in a single location.
The small Yellowstone quakes are not considered to pose a threat to the public, but are of great interest to scientists who want to confirm if they were triggered and understand how. Investigation is ongoing and may take some time to complete, said Sue Nava, seismograph network manager at the University of Utah Seismograph Stations.
There has been some suggestion that seismic waves from a large, distant quake may jostle the ground at Yellowstone, triggering small quakes by moving the hydrothermal fluids responsible for Yellowstone geysers and hot springs.
Those wishing to view seismograms of the Alaska earthquake and those in Yellowstone recorded on the Yellowstone seismic network may go to the web site: http://www.seis.utah.edu/helicorder/heli/yellowstone/index.html
The U.S. Geological Survey's National Earthquake Information Center website has information on the Alaskan earthquake that can be viewed at: http://neic.usgs.gov/neis/bulletin/neic_lbbl.html
The Yellowstone seismic network is operated by the University of Utah Seismograph Stations as a partner in the Yellowstone Volcano Observatory (YVO). Information on YVO and earthquake activity in Yellowstone can be found at: http://volcanoes.usgs.gov/yvo/