[CEUS-earthquake-hazards] Comment on "major" earthquake

[Seth Stein]

The term "major" earthquake is typically used in textbooks, etc. for 
magnitude greater than 7

http://en.wikipedia.org/wiki/Richter_magnitude_scale

In the New Madrid zone the last was in 1812. A magnitude 6 occurs on 
average about every 100-150 years.

It's interesting to read the accounts of the 1895 (M estimated as 
6.0-6.6) earthquake, the largest since 1812

http://earthquake.usgs.gov/regional/states/events/1895_10_31.php

and the 1968 (M ~ 5.5) earthquake

http://earthquake.usgs.gov/regional/states/events/1968_11_09.php

In both, most of the damage occurred in an area close to the epicenter 
of intensity VII (moderate damage) consisting of "downed chimneys, 
cracked walls, shattered windows, and broken plaster," and lesser 
effects further away.

This is obviously not good, but it's probably not what the public would 
regard as a "major" disaster. It's worth noting that if everyone 
involved had had earthquake insurance with a 15% deductible

http://www.stltoday.com/stltoday/news/columnists.nsf/savvyconsumer/story/FA8B07211D6155BD8625743600105DFE?OpenDocument

few would have collected.

Of course one could conceive of locations in the New Madrid zone where 
if such an earthquake happens to hit damage would be greater

-- 
Seth Stein
William Deering Professor
Department of Earth and Planetary Sciences
1850 Campus Drive
Northwestern University, Evanston, IL 60208
(847) 491-5265 FAX: (847) 491-8060 E-MAIL: seth at earth.northwestern.edu
http://www.earth.northwestern.edu/people/seth


>   
>    With so much to learn about earthquakes, we all should take care to 
> be consistent and not overstate what is known.  A quoted seismologist in 
> discussing the 18 APR 08 Mount Carmel, IL event said "we don't to worry 
> about a */MAJOR /*[highlighted for emphasis] New Madrid earthquake for 
> another 300 years."  It is my understanding that we are overdue for a 
> low M6 event (yet not 100% likelihood in 10 years) in the New Madrid 
> region.  A major event and a low M6 is too casual of use and certainly 
> feeds the misinformation to the public, because of a slip of the tongue. 
>