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February 19, 2008
By John Trent
The Nevada and eastern California region experienced one of its quietest years on record for earthquake activity, according to a study by the University’s Nevada Seismological Laboratory.
Nevada seismologists located only 4,503 earthquakes during 2007 in their monitoring region that includes Nevada and eastern California; only three of 2007’s earthquakes were magnitude 4.0 or larger. These events occurred in relatively remote areas, with the largest, north of Bridgeport, Calif., on March 9, registering a 4.9. The largest within the borders of Nevada was a magnitude 4.1 earthquake on Jan. 24, 2007, about 25 miles south-southeast of Goldfield.
“Because earthquakes form a complicated pattern in space and time, there is no simple way to rank the calendar years based on the rate of activity,” said John Anderson, director of the Nevada Seismological Laboratory, which is a research and academic unit within the College of Science’s Mackay School of Earth Sciences and Engineering. “But by any ranking, 2007 was one of the quietest on record.”
Since 1932, the average year for the region has had about 18 earthquakes with magnitude 4.0 or greater, making the three in 2007 represent about 17 percent of the average. 2005 was also another quiet year, with only two earthquakes larger than magnitude 4.0.
The numbers for a quiet seismological year are also borne out by looking at earthquakes with magnitude 3.0 or greater. 2007 had 36 such events, which compares to the quietest years on record, 1977 and 2005, when there were only 31 events at 3.0 or greater.
Anderson said it is difficult to forecast what is in store for 2008.
“Low rates of activity in 1945 and 1989 were not immediately followed by exceptionally active years, so the low level of seismicity in 2005-2007 does not necessarily imply that 2008 will be more active,” he said.
The veteran seismologist noted that although short-term prospects for earthquake activity cannot be predicted, Nevada has not had an earthquake with a magnitude greater than 7.0 since 1954. Based on earthquake activity since the mid-1800s, it should be expected that at least one such major event should occur on average every 25 or 35 years, he said.
“A magnitude-7.0 earthquake could occur almost anyplace in Nevada, but is more likely in areas where smaller earthquakes are more common,” Anderson said, adding that mapping and historical trends indicate that western Nevada has higher rates of smaller earthquakes. “Because we cannot forecast or predict where the next damaging earthquake will occur, Nevadans are always urged to be prepared for potentially damaging events.”
The Nevada Seismological Laboratory is the lead agency in monitoring earthquakes in the western Great Basin, as part of a nationwide monitoring program that is supported by the U.S. Geological Survey. It is part of an exclusive group of universities that contribute in major ways to the nation’s monitoring network.
Earthquake preparedness information is available from the Nevada Seismological Laboratory.