Earthquakes 20 Miles Deep Lift Mountain A Few Millimeters
A cluster of small earthquakes this summer about 20 miles below Lake Tahoe has caused an unprecedented eight millimeter uplifting of a ski resort mountain in the Sierra Nevada, researchers have discovered.
Some 1,600 small earthquakes 20 miles beneath Lake Tahoe, the world’s second-largest alpine lake, from August 12, 2003 through February 19, 2004 and then stopped, eyewitnesses report.
Based on observations from the university’s Nevada Seismic Network and an ultra-sensitive Global Positioning System (GPS) station at Slide Mountain, the researchers believe the quake cluster coincided with an unprecedented eight millimeter uplifting of the Slide Mountain ski resort mountain in the Sierra Nevada.
“We’ve been watching earthquakes for 30 years in the Tahoe area and have never witnessed an earthquake swarm anything like this,” said Ken Smith, research seismologist at the university’s Nevada Seismological Laboratory and principal author of an article to be published in August in the journal, “Science,” and on its website
“We haven’t seen any more deep earthquakes or notable movement at the Slide Mountain GPS station since,” Smith said.
Geoff Blewitt, a research geophysicist with the university’s Nevada Bureau of Mines and Geology and co-author of the “Science” article, said the uplift at Slide Mountain “can be explained by the movement of magma about 20 miles deep, which forced several miles of rock apart by about one meter.”
He added that he and his colleagues believe the rapid growth of this fissure caused the series of earthquakes – no greater than magnitude 2.2 – that caused the mountain to rise.
The eastern side of the Sierra Nevada is the West’s third most seismically active area behind only Alaska and the San Andreas fault system in California. Scientists note that over the past several million years, Lake Tahoe itself has been created by repeated earthquakes on the West Tahoe Fault, which runs along the lake’s bottom and western side.
The eastern front of the Sierra Nevada represents one of the fundamental tectonic boundaries in the United States. The mountain range moves at a rate of about 12 to14 millimeters per year to the northwest. Researchers believe the deep event observed at Lake Tahoe is part of the process of the evolution and westward growth of the Basin and Range Province.
The university is a member of the National Science Foundation’s Network for Earthquake Engineering Simulation, an exclusive group of only 15 universities involved in carrying out research and obtaining information vital for reducing the nation’s vulnerability to catastrophic earthquakes.
Provided by the Environmental News Service.