INVESTIGATION OF POSSIBLE PALEOLIQUEFACTION FEATURES IN MISSISSIPPI

 

Hanan H. Mahdi1*, Haydar J. Al-Shukri1, Robert E. Lemmer1, Jeffrey B. Connelly1, and Michael B. E. Bograd2, 1University of Arkansas at Little Rock and 2Mississippi Office of Geology, Jackson, MS 39289

 

      Mississippi is in a mid-plate region of infrequent strong earthquakes. The active New Madrid Seismic Zone, close to northwestern Mississippi, poses the greatest risk to the state from earthquakes. In a region of infrequent earthquakes and a short historical record, we must resort to a search for physical evidence of past strong earthquakes. Investigation is under way in northwestern Mississippi of possible paleoliquefaction features (old sand blows resulting from earthquake-induced liquefaction). Sites in Tunica County, Mississippi, bear the same signature on satellite imagery as sites in Arkansas confirmed to be paleoliquefaction features. Agricultural fields on 1962 aerial photographs of Tunica County show circular patches of light color that could be more reflective sand surrounded by darker alluvial soils. Field investigations during the dry summer of 2000 screened sites worthy of further work. The next step will be profiling each feature with hand-auger and collecting ground-penetrating radar data. If these investigations indicate possible sand-blow features, the sites will be trenched, and attempts will be made to determine the age of the features. If these are indeed earthquake-induced sand blows, the implications for earthquake risk to Mississippi are significant. Perhaps the New Madrid earthquakes of 1811-1812 were stronger than now understood, or there was a strong earthquake farther south than any now known.