NEW MADRID PLATE GEOMETRY

CARNEY, M., INCA Engineers, Bellevue, WA 98004, mycarney@earthlink.net.

The tectonic mechanism causing the seismic activity around New Madrid has

not been clearly delineated or widely accepted. This paper proposes a pattern of tectonic plate movement that agrees with the observed seismic behavior around New Madrid. It also agrees with surrounding geology and topography. The historical earthquakes point to a spreading motion. Many lakes and sunken areas were created. The connection in time with seismic activity at Charleston could be explained if New Madrid and Charleston are at points of maximum motion,rotating about a point midway between them. Rotating motion would explain why the land between them has seen less seismic activity. The edge and depth of the Mississippi embayment compared to the older

surrounding rock edges could be explained as river sediment filling in where a fault occurred. Dating the cracks to the north of New Madrid with the oldest fill on the eastern edge puts the major crack 200-300mybp, which would be the time of the breakup of Pangea. There have been subsequent motions, but they seem to be tapering off in geologic time.Reconstructing the land prior to the separation, matching similar geology

and topography, the Appalacian/Cumberland chain appears to join the Ozarks. The wedge, defined by New Madrid, the southern tip of Florida and Charlestown, appears like a shard splaying off of the main line of separation. In the break up of Pangea, separation might have occurred inland of the Appalacians thru New Madrid. Instead the land masses tore apart on the eastern side of the Appalacians. There is extensive open jointing of bedrock east of the Mississippi embayment north of the Appalacians that is consistent with this theory. The open joints point to a distributed tearing in the surface which would occur with the proposed motion of the south end of the Appalacians.