LOPEZ, JOHN A.*, SHEA PENLAND, and JEFF WILLIAMS

Active geologic faults in Lake Pontchartrain have been previously described in 1991. These faults have apparent surface expression and strongly suggests that at least some of these faults are active faults. The en echelon fault system in Lake Pontchartrain are the southeastward continuation of the active Baton Rouge - Denham Springs faults system in the Baton Rouge area. New documentation of faulting includes: 1) GPS positioning of bridge offsets 2) acquisition of US Geological Survey high resolution seismic 3) more complete mapping of faults 4) new quantification Railroad and bridge offset at fault traces.

The US Geological Survey high-resolution seismic data demonstrate geologic faults with offset within 30 ft of the Lake bottom in the eastern portion of the Lake. However, the high resolution seismic positioned parallel to the Causeway does not detect a fault at the offset in the Causeway bridge. It is possible the fault offset is too small to be resolved.

Recent observations suggests possibly higher rates of fault movement than previously suggested. In particular the Southern Railroad bridge has shown 2-3 inches offset at the southern fault position where the bridge was re-built in 1986 and 1987. The northern fault trace shows similar new offset of the Southern railroad bridge. This suggest a rate of fault displacement 2-3 times higher than suggested in 1991 by monitoring and observation at that time.

AAPG Search and Discovery Article #90941©1997 GCAGS 47th Annual Meeting, New Orleans, Louisiana