From: "Andrew J. Miller" <miller@umbc.edu>

Newsgroups: umbc.course.geog110h

Subject: Re: Assignment #8 Note...(#9 info also)

Date: Thu, 17 Apr 1997 23:56:28 -0400

Matt Allen wrote:

>

It was interesting to see

> that there have been numerous earthquakes originating in various > locations here on the East coast. A large number of these are located > along the Mississippi between Missouri and Kentucky. I am curious to > see what relationship exists between this area and the relative > abundance of earthquakes in the Eastern U.S. which originate there. The frequency and magnitude of these quakes don't compare to those of the Western United States, but the fact that they do occur seems intriguing.

Try these pages, which talk about the New Madrid earthquakes that occurred in Missouri in 1811-1812:

http://gandalf.ceri.memphis.edu/~rwilk/slides.html

http://www.ceri.memphis.edu/www/public_info/faultfacts.html

http://www.eas.slu.edu/Earthquake_Center/earthquakecenter.html

And here's a pretty good general page of earthquake links that I hadn't seen before. Also, if you're interested, you might check out the virtual field trips from the set of green buttons on the upper left side of the page.

http://www.geologylink.com/toc/chap10.html

Another general-interest USGS earthquake page:

http://quake.usgs.gov/

Here's some stuff from a USGS publication that's also relevant:

(source: http://pubs.usgs.gov/publications/text/tectonics.html )

Mid-plate earthquakes -- those occurring in the interiors of plates -- are much less frequent than those along plate boundaries and more difficult

to explain. Earthquakes along the Atlantic seaboard of the United States are most likely related in some way to the westward movement of the North American Plate away from the Mid-Atlantic Ridge, a continuing process begun with the break-up of Pangaea. However, the causes of these infrequent earthquakes are still not understood.

East Coast earthquakes, such as the one that struck Charleston, South Carolina, in 1886 are felt over a much larger area than earthquakes occurring on the West Coast, because the eastern half of the country is mainly composed of older rock that has not been fractured and cracked by frequent earthquake activity in the recent geologic past. Rock that is highly fractured and crushed absorbs more seismic energy than rock that

is less fractured. The Charleston earthquake, with an estimated magnitude of about 7.0, was felt as far away as Chicago, more than 1,300 km to

the northwest, whereas the 7.1-magnitude Loma Prieta earthquakes was felt no farther than Los Angeles, about 500 km south. The most widely felt earthquakes ever to strike the United States were centered near the town of New Madrid, Missouri, in 1811 and 1812. Three earthquakes, felt as far away as Washington D.C., were each estimated to be above 8.0 in magnitude. Most of us do not associate earthquakes with New York City, but beneath Manhattan is a network of intersecting faults, a few of which are capable of causing earthquakes. The most recent earthquake to strike New York City occurred in 1985 and measured 4.0 in magnitude, and a pair of earthquakes (magnitude 4.0 and 4.5) shook Reading, Pennsylvania, in January 1994 causing minor damage.

And these comments about the Charleston, South Carolina earthquake of 1886 don't help much but they are interesting:

http://www.sc.edu/usctimes/16nov95/4.html