FAULTING ALONG THE SOUTHERN MARGIN OF REELFOOT LAKE, TENNESSEE

The Reelfoot Lake basin, Tennessee, is structurally complex and of gre at interest seismologically because it is located at the junction of t wo seismicity trends of the New Madrid seismic zone. To better underst and the structure at this location, a 7.5-km-long seismic reflection p rofile was acquired on roads along the southern margin of Reelfoot Lak e. The seismic Line reveals a westerly dipping basin bounded on the we st by the Reelfoot reverse fault zone, the Ridgely right-lateral trans pressive fault zone on the east, and the Cottonwood Grove right-latera l strike-slip fault in the middle of the basin. The displacement histo ry of the Reelfoot fault zone appears to be the same as the Ridgely fa ult zone, thus suggesting that movement on these fault zones has been synchronous, perhaps since the Cretaceous. Since the Reelfoot and Ridg ely fault systems are believed responsible for two of the main-shocks of 1811-1812, the fault history revealed in the Reelfoot Lake profile suggests that multiple mainshocks may be typical of the New Madrid sei smic zone. The Ridgely fault zone consists of two northeast-striking f aults that lie at the base of and within the Mississippi Valley bluff Line. This fault zone has 15 m of post-Eocene, up-to-the-east displace ment and appears to locally control the eastern limit of Mississippi R iver migration. The Cottonwood Grove fault zone passes through the cen ter of the seismic line and has approximately 5 m of up-to-the-east di splacement. Correlation of the Cottonwood Grove fault with a possible fault scarp on the floor of Reelfoot Lake and the New Markham fault no rth of the lake suggests the Cottonwood Grove fault may change to a no rtherly strike at Reelfoot Lake, thereby linking the northeast-trendin g zones of seismicity in the New Madrid seismic zone.