| MadSci Network: Earth Sciences |
The Illinois State Geological Survey: http://www.isgs.uiuc.edu/isgshome/isgshome.html has some useful information on your question - I had to do a little digging around to find the right group, but the Sedimentary and Crustal Processes Section is it. They are at: http://www.isgs.uiuc.edu/sedcrust/sedhome.html Among the things I found was a map of quakes, including two medium sized ones in southern Illinois: http://www.isgs.uiuc.edu/sedcrust/mcearth.jpg There are symbols next to each of these that look a bit like a beach ball (large circle separated into black and colorless parts). These are first motion diagrams that show how the fault moved. The dark parts represent directions in which the first motions compressed the rock. For the 1968 earthquake, the fault had thrust fault motions and the fault plane trends nearly north-south and slopes either moderately to the east or moderately to the west (first motion diagrams always have two possible fault solutions). The 1974 earthquake is on a strike-slip fault and the motion is either left-lateral (when you look across the fault the other side moves to the left) on a nearly vertical fault trending northwest or right-lateral on a nearly vertical fault trending northeast. The cluster of tiny earthquakes nearby that also trend to the NW might tend to support the first interpretation, but I don't have any way of confirming that. The faults of the New Madrid zone and nearby areas are all very old, with a long and complex history. Many of them are not easily seen at the surface and so identifying possible fault hazards becomes very difficult. The seismic map shows a large number of small quakes in southern Illinois that lack a clear pattern. This is an area where more research needs to be done (and is being done by the Illinois survey). Geologic maps of the quadrangles in your area are available from the Illinois survey and will have more information, including the traces of any faults that are known. Maybe your teacher can order these, or you can find them at a library. The best place to try is in college science libraries (most public libraries don't cary geologic maps, although you can always ask). Here are some other web resources on New Madrid that may be of assistance: The USGS Fact Sheet on the New Madrid Zone - it has some links to maps of quakes and hazards: http://quake.wr.usgs.gov/prepare/factsheets/NewMadrid/ The Center for Earthquake Research and Information in Memphis. They have hazard and other information, including maps of recent quakes http://www.ceri.memphis.edu/ Good luck with your project, David Smith Geology & Environmental Science La Salle University, Philadelphia, PA
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