Earthquake signals in tree-ring data from the New Madrid seismic zone and implications for paleoseismicity
Severe ground shaking and the formation of Reelfoot Lake during the great New Madrid earthquakes of <span class="smallcaps">a.d.</span> 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. Ground 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 sunkland of northeastern Arkansas was severely suppressed for almost 50 yr following the 1811 1812 New Madrid earthquakes. Thus, there are two opposite but profound growth responses to the same earthquake events preserved in baldcypress trees of the New Madrid seismic zone. The tree-ring chronology at Reelfoot Lake extends from <span class="smallcaps">a.d.</span> 1682 to 1990, but the 1812 1819 growth surge was the only extreme growth anomaly in this 309 yr period. The St. Francis sunkland chronology extends from <span class="smallcaps">a.d.</span> 1321 to 1990, and the 1812 1857 growth suppression is the most severe and prolonged growth anomaly of this entire 670 year period. Thus, the tree-ring record indicates that there was not a great earthquake during the 129 yr prior to 1811 in the Reelfoot Lake basin, nor during the 490 yr prior to 1811 in the St. Francis sunkland.