Bootheel Lineament, the elusive surface rupture of the New Madrid Seismic Zone?
by
Margaret J. Guccione
Dept. of Geosciences, OZAR-113, University of Arkansas, Fayetteville, AR 72701 USA
Coauthors: Ron Marple (WesternGeco, Houston TX 77042 USA)

Three great earthquakes during the winter of 1811-1812 had a felt area of more than 1500 km from the epicentral area in the northern Mississippi alluvial valley. These catastrophic earthquakes, approximately a month apart, caused extensive liquefaction, ground failure and bank caving, landslides along river bluffs, and surface deformation large enough to impact the flow of the Mississippi River, impound a creek to form Reelfoot Lake, and uplift a dome above normal flood level of the Mississippi River flood plain. Though the estimated magnitudes of the earthquakes are between 7 and 8+, no definitive surface rupture has been identified. Instead, the seismic zone is delineated by microseismicity measured during the last several decades and the domal uplift has been identified as fault-related folding in a transpressive zone of a strike slip fault.

It is unusual for seismic events with relatively shallow foci and magnitudes the size of the 1811-1812 New Madrid earthquakes not to have surface rupture. The Bootheel lineament, a linear 135 km-long feature subparallel to the New Madrid seismic zone, has been identified as a potential rupture but extensive liquefaction along the lineament has made tectonic offset difficult to prove. A infilled paleochannel east of the lineament is visible on aerial photographs but is truncated by the lineament and not obvious west of the lineament. Detailed coring on both sides of the lineament supports the hypothesis that the lineament is a surface rupture and that it is coincident with liquefaction. The channel on the west side of the lineament appears to be laterally offset approximately 10-12 m to the north and vertically offset approximately 2 m in at least one event or sequence of events. The two meters of liquefied sand and clay that fill a depression >100 m wide west of the lineament obscure the paleochannel west of the lineament.

Beyond the area of liquefaction and ground failure, the Mississippi River overbank clay is >3 m thicker west of the lineament than it is east of the lineament, indicating > 3 m of vertical movement along the fault during the Holocene. Adjacent to the lineament the clay is split by liquefied sand and fluvial deposits, suggesting at least two rupture episodes.

Date received: March 10, 2002