GRANTS PASS, Ore. – Scientists say a swarm of earthquakes since July in the remote desert linking Oregon, California and Nevada can be traced to the constant stretching of the Earth's crust.
The Sierra Nevada is moving northwest about a half-inch a year, leaving gaps in Nevada's northwestern corner, where one fault has produced hundreds of small quakes, Glenn Biasi of the University of Nevada Seismological Laboratory said Tuesday.
Similar swarms beneath populated areas have culminated in quakes in the magnitude 5.0 range that have cracked walls and toppled chimneys. However, the desert swarm is so remote that damage is unlikely.
The swarm has generated more than 800 tremors that registered on seismographs but were rarely felt by people. The two biggest shakers came last week and were measured at magnitude 4.7.
WHERE IS THE SWARM?
The swarm is centered in the northwest corner of Nevada about 40 miles southeast of Lakeview, Oregon, in a dusty plain of dry alkali lakebeds called Long Valley. The Sheldon National Wildlife Refuge and the Summit Lake Indian Reservation are to the east. The Black Rock Desert is to the south.
HOW BIG IS IT?
The area measures about 7 miles long and about 2 miles at its widest point. There are no nearby instruments to give a good idea just how deep it is, but Biasi said it is likely 3 or more miles below the surface.
DID ANYONE FEEL IT?
Probably. But there are just not many people out there. Gina Barr at the wildlife refuge headquarters in Lakeview didn't feel it. Neither did Morgan Bryson at the Denio Motel, about 50 miles to the east. The one man who lives at the Sheldon refuge did, but he is gone for a month's vacation, Barr said. "It's one of those corners of Nevada where a blind man could run an artillery school without hurting anyone," Biasi said.
WHAT WOULD IT FEEL LIKE?
Even the biggest of the quakes was not big enough to shake you out of a lawn chair if you were sitting right on top of it, Biasi said.
WHAT IS THE POTENTIAL FOR A BIGGER QUAKE?
The fault moves up on one side and down on the other and covers a distance of about 30 miles. If it all let loose at once, it could produce a magnitude 7.0 quake, but that is very unlikely, Biasi said.
DOES THE SWARM MEAN A BIGGER QUAKE IS COMING?
Some swarms in the past have culminated in larger quakes before settling down, but it is impossible to say if this one will. In 2008, a swarm west of Reno, Nevada, included a magnitude 5.0 temblor that cracked walls in about 100 houses in the bedroom community of Mogul, Nevada. Pictures were knocked off walls, furniture was upended, and glassware was broken. Overall damage was estimated at $1 million.
WHERE CAN I LEARN MORE?
The U.S. Geological Survey has an interactive online map at http://earthquake.usgs.gov/hazards/qfaults/map/ that shows all the known faults in the country. You can see on the map that the Sierra Nevada has few, but there are lots to the north, where the mountains smoosh up against the Cascade Range.