Paleo-Seismic Activity from the NEW Madrid Seismic Zone Recorded IN Stalagmites. A NEW Tool for Paleo-Seimic History

As the 200th anniversary of the 1811-1812 earthquakes of the New Madrid Seismic Zone (NMSZ) approaches, recent seismic activity in southern Illinois (magnitude 5.2) and a devastating earthquake of magnitude 7.9 in eastern Sichuan China have drawn attention to the need for additional techniques for studying seismic zones. Currently, the paleo-seismic history of the NMSZ is being reconstructed using sand blows and sand dikes, landslides, and Mississippi River floodplain deposits. A new technique being developed by the authors indicates that the time of initiation and/or regrowth of stalagmites in caves located within the magnitude 6 isoseismal line of a seismic zone may be dominated by seismic activity. Consequently, the paleo-seismic history of the NMSZ and any other seismic zone in the vicinity of active caves may be reconstructed using this technique.

We are currently sampling 60 stalagmites from caves in southern Illinois, and southeastern Missouri in order to determine the timing of their initiation. For dating purposes, we are using U/Th techniques and, for the very young stalagmites (200 years BP or less), a combination of U/Th dating and growth laminae counting. Preliminary results of this work and the available published dates of stalagmite initiation in Illinois and Missouri caves correspond to historic and prehistoric seismic events. The dates of initiation for stalagmites collected thus far occurred 200 +/- 50 (n = 5), 1178 +/- 17 (n = 2), 3500 +/- 100, 3,900, 4600 +/- 110 (n = 2), 5500 +/- 240 (n = 2), 11,284 +/- 70, and 17,840 +/- 120 years BP (n = 1 if not indicated). Each of these dates, within limits of analytical error, correspond with known earthquakes associated with the NMSZ determined by others using sand blows and landslides. Additional results from this investigation will be presented at the time of the meeting.