Earthquakes in Minnesota
From: Tim Salo Date: 3:55am, Mar 31, 2009
Apparently, the risk of earthquakes is yet another reason to oppose the Crown Hydro project. WIZARD MARKS wrote: > ... Would that my argument could be dismissed as NIMBY, but it > cannot. I don't live on the river, worse luck, but the reasons > for keeping this project off the space where Crown wants it to > be are much deeper, and a great deal more important, than NIMBY. > > We have all witnessed the aftermath of Hurricane Katrina, ... I will let someone else explore the risk that hurricanes, volcanoes and tsunamis pose to the proposed Crown Hydro project... > As well, this particular river is on the New Madras Fault Line > and while the fault line has not kicked up a major fuss since > the 1870s, it does have minor tremors and could, of course, have > another major shake up. ... Apparently, the New Madrid Fault has also been "implicated" in the imminent collapse of a bridge, as well. dyna wrote: > Wizard, thank you for your observations of the structural > instability of the river. I'd completely forgotten about the New > Madrid fault, and perhaps the geologic trauma you've noted may > explain the shifting of the Lowry Avenue Bridge's pillars that > threaten to dump those venerable trusses into the river. ... Never mind that the New Madrid fault zone is nowhere near Minneapolis... The University of Arkansas Seismic Observatory has a whole page of links devoted to the New Madrid Fault Zone: <http://quake.ualr.edu/public/nmfz.htm> Of possible relevance: "The New Madrid Seismic zone lies within the central Mississippi Valley, extending from northeast Arkansas, through southeast Missouri, western Tennessee, western Kentucky to southern Illinois. Historically, this area has been the site of some of the largest earthquakes in North America. <http://www.eas.slu.edu/Earthquake_Center/SEISMICITY/NewMadridGeneral.html> A nice picture of the location of known earth quakes in the area is available at: <http://www.ceri.memphis.edu/aware/nmsz.html> The USGS has a page on the New Madrid fault zone: <http://quake.wr.usgs.gov/prepare/factsheets/NewMadrid/> The USGS even has a nice map of the area affected by the 1895 magnitude 6.8 New Madrid earth quake: <http://quake.wr.usgs.gov/prepare/factsheets/NewMadrid/Charleston1895.gif> The mere fact that the location of the proposed Crown Hydro project wasn't seriously affected by a major quake on the New Madrid fault shouldn't deter critics of the Crown Hydro project. Of course, this this doesn't _prove_ that an earth quake _couldn't_ happen in Minneapolis. The USGS (yes, yes, I know, it's part of the U.S. government and therefore automatically suspect by some on this list) even has information about earthquakes in Minnesota: <http://earthquake.usgs.gov/regional/states/?region=Minnesota> According to the USGS, the "largest earthquake in Minnesota" "caused minor damage to walls and foundations of basements in Stevens County around Morris". No word of bridge or dam collapses. They even have a nice seismic hazard map for Minnesota: <http://earthquake.usgs.gov/regional/states/minnesota/hazards.php> The emergency preparedness and conspiracy folks may also want to look at the DNR's page on volcanoes, earthquakes, and glaciers in Minnesota: <http://www.dnr.state.mn.us/education/geology/digging/index.html> More than you ever wanted to know,
From: Carol Becker Date: 11:49am, Mar 31, 2009
Personally I think it is way cool that the earth is still rebounding from the heavy weight of glaciers... Quoted from the State of Minnesota Yellow Pages at http://www.yellowpages.state.mn.us/is/yellowpages.nsf/059eefc5b0cd22be86256b21007e2c0e/dd278fbcabeea44a86256b1f0059907e?OpenDocument "In the 141 years since 1860, Minnesota has recorded 18 earthquakes, more than half of them during the last 35 years. Most of Minnesota's earthquakes occur along a line that runs from the southwest to the northeast through Ortonville, Morris, Alexandria, Staples and Nisswa. This area is part of the Great Lakes Tectonic Zone, which, along with the Yellow Medicine Shear Zone, was formed more than 2 billion years ago. They are called zones instead of faults because the exact location is hard to pin down, but runs in about a 30-mile wide band situated on the basis of earthquakes that have occurred in the past. The North American continent sits on a plate that is gradually moving westward, experiencing slippage on various fault lines and causing earthquakes. Faults are fractures in the rocks where pressure in the earth's crust tends to be released. One theory says today's Minnesota quakes are caused by glacial unloading. This is the rebounding of areas depressed by the weight of glaciers that buried Minnesota and much of the Dakotas about 12,000 years ago. The glaciers - over a mile thick - depressed the earth under their massive weight. Earthquakes measuring less than 5.0 on the Richter scale are generally considered minor quakes and cause little damage. About 6,200 minor quakes occur each year around the globe. Each increase in a whole number on the Richter scale represents a 10-fold increase in power and a 30-100 times increase in energy released. Damage usually occurs with magnitude 5-5.9 quakes. There are about 800 earthquakes around the world in that range every year. Only the few earthquakes that measure 6.5 and above have the ability to cause severe property damage and the loss of large numbers of lives. An earthquake registering between 7 and 8 on the Richter scale is classified as major, while anything higher than 8 qualifies as great. An earthquake, measuring about 4.7 on the Richter scale, occurred on July 10, 1975 in the neighboring towns of Alberta and Morris. No damages or injuries were reported. In June 1987, an earthquake registering 4.1 in Lawrenceville in southeastern Illinois was felt in southeastern Minnesota. The most recent quake felt in Minnesota occurred on October 20, 1995, centered next to the Minnesota border near Rosholt, S.D. The only recorded earthquake damage suffered in the state came in 1917 when a quake centered in Staples, registering 4.3 on the Richter scale, knocked down some chimneys. The most powerful quake in Minnesota was in 1860 and was estimated at 5.0. The Richter Scale was not invented until 1935. Below is a list of recorded quakes felt in Minnesota: Earthquakes in Minnesota: Date, Epicenter, County, Magnitude Date Epicenter County Magnitude 1860 Long Prairie Todd 5.0 Dec. 16, 1860 New Prague Scott 4.7 Dec. 28, 1880 St. Vincent Kittson 3.6 Feb. 6, 1917 Red Lake Beltrami 3.6 Sept. 3, 1917 Staples Todd 4.3 Dec. 23, 1923 Bowstring Itasca 3.8 Jan. 28, 1939 Detroit Lakes Becker 3.9 Feb. 15, 1950 Alexandria Douglas 3.6 Sept. 28, 1964 Pipestone Pipestone 3.4 July 9, 1975 Morris Stevens 4.7 Mar. 6, 1979 Milaca Mille Lacs 1.0 April 16, 1979 Evergreen Becker 3.1 May 14, 1979 Rush City Chisago 1.0 July 26, 1979 Nisswa Crow Wing 1.0 April 24, 1981 Cottage Grove Washington 3.6 Sept. 27, 1982 Walker Cass 2.0 June 1987 Lawrenceville Lawrence, Ill. 4.1 June 4, 1993 N.W. of Morris Stevens 4.1 Feb. 9, 1994 N. of Granite Falls Yellow Medicine 3.1 Oct. 20, 1995 Rosholt, Roberts, S.D. 3.7 For more information, contact the Minnesota Geological Survey, 2642 University Ave., St. Paul, MN 55114-1057" Carol Becker Longfellow A geek about many things
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