John Lopez¹
(1) N/A, Slidell, LA

Abstract: Confirmation of active geologic Faults in Lake Pontchartrain in Southeast Louisiana

The en-echelon fault system in northern Lake Pontchartrain is the southeastward continuation of the active Baton Rouge - Denham Springs fault system in the Baton Rouge area. Modern movement of these faults was proposed in 1991. These faults have apparent surface expression which suggests that at least some of these faults are active. New documentation of faulting includes: 1) Global Positioning System was used to locate bridge offsets 2) acquisition of US Geological Survey high resolution seismic 3) more complete mapping of faults and, 4) new quantification of Railroad and bridge offset at fault traces.

US Geological Survey high-resolution seismic profiles demonstrate two geologic faults with offset within the Holocene within 10 feet of the Lake bottom in the eastern portion of the Lake. In contrast, one high resolution profile positioned parallel to the Causeway does not indicate a fault.

Recent observations suggest possibly higher rates of fault movement than previously recognized in Lake Pontchartrain. In particular, a railroad bridge has shown 3-4 inches offset at the southern fault position where the bridge was re-built in 1986 and 1987. The northern fault trace shows a similar new offset of the Southern railroad bridge. This suggests a rate of fault displacement two to three times greater than suggested by previous observations.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana