EARTHQUAKE SIGNALS IN TREE-RING DATA FROM THE NEW MADRID SEISMIC ZONEAND IMPLICATIONS FOR PALEOSEISMICITY

Severe ground shaking and the formation of Reelfoot Lake during the gr eat New Madrid earthquakes of A.D. 1811-1812 had a profound effect on baldcypress trees that still survive in Reelfoot Lake of northwestern Tennessee. Inundation greatly increased baldcypress radial growth from 1812 to 1819 and permanently decreased wood density after 1811. Groun d shaking fractured the baldcypress stems that were present during the 1811-1812 event, but fractures are absent in the post-1811 growth. In contrast, the growth of old baldcypress trees in the St. Francis sunk land of northeastern Arkansas was severely suppressed for almost 50 yr following the 1811-1812 New Madrid earthquakes. Thus, there are two o pposite but profound growth responses to the same earthquake events pr eserved in baldcypress trees of the New Madrid seismic zone. The tree- ring chronology at Reelfoot Lake extends from A.D. 1682 to 1990, but t he 1812-1819 growth surge was the only extreme growth anomaly in this 309 yr period. The St. Francis sunkland chronology extends from A.D. 1 321 to 1990, and the 1812-1857 growth suppression is the most severe a nd prolonged growth anomaly of this entire 670 year period. Thus, the tree-ring record indicates that there was not a great earthquake durin g the 129 yr prior to 1811 in the Reelfoot Lake basin, nor during the 490 yr prior to 1811 in the St. Francis sunkland.