Stretching crust causing quakes in remote Nevada
Posted: Friday, November 14, 2014
GRANTS PASS, Ore. (AP) — 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 Wednesday.
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, Ore., 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?
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.
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, Nev., included a magnitude 5.0 temblor that cracked walls in about 100 houses in the bedroom community of Mogul, Nev. Pictures were knocked off walls, furniture was upended, and glassware was broken. Overall damage was estimated at $1 million.
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.
So, are these quakes then related to those in Northern Nevada hat have been occurring lately? Jim
-----Original Message-----
From: californiadisasters@yahoogroups.com [mailto:californiadisasters@yahoogroups.com]
Sent: Saturday, November 15, 2014 9:24 AM
To: undisclosed-recipients:
Subject: [californiadisasters] Quake swarm near Lassen Peak doesn't appear to be volcanic
Quake swarm near Lassen Peak doesn't appear to be volcanic
Staff Reports
Posted: 11/14/2014
Click photo to enlarge
<http://www.chicoer.com/portlet/article/html/render_gallery.jsp?articleId=26942012&siteId=135&startImage=1>
Screen shot of the U.S. Geological Survey's earthquake website (http://earthquake.usgs.gov) shows...
LASSEN PARK >> A hundred years ago the ground around Lassen Peak was shaking, as the volcano was in the midst of a year-long string of small eruptions that would culminate with an explosive eruption May 22, 1915.
The ground in that vicinity had been shaking again for the last week, although scientists don't think it's related to volcanic activity.
Since Nov. 8, there have been in excess of 150 densely-packed earthquakes just south of Lassen Volcanic National Park. Almost all the quakes have been tiny, with just a handful that could be felt even under favorable conditions. The largest was a 3.86 magnitude quake that happened just after midnight on Nov. 11.
The quake swarm has been concentrated in a band between Mill Creek and the North Fork of the Feather River, between Lassen Park and Childs Meadow. As of 5 p.m., there had been seven quakes on Friday, ranging from magnitude 2.7 to 1.6.
A call to the U.S. Geological Survey seeking comment was not returned by deadline, but the website of its California Volcanic Observatory indicated the swarm's cause doesn't appear to be volcanic activity. "Ground deformation indicative of volcanic unrest has not been detected by nearby GPS receivers," the website states.
Instead the quakes are likely fault motion along the Walker Lane Fault System, which runs near the California-Nevada border. No immediate threat is seen.
The Volcanic Observatory is in contact with Lassen Park, however, watching for any changes in the hydrothermal features there.
http://www.chicoer.com/news/ci_26942012/quake-swarm-near-lassen-peak-doesnt-appear-be
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