MAJOR ACTIVE FAULTING ALONG THE LOUISIANA “PASSIVE” MARGIN REVEALED BY LIDAR MAPPING AND GEODETIC LEVELING

The east-west Baton Rouge fault of south Louisiana is part of a belt of down-to-the south normal faults that form the northernmost structures of the active Gulf of Mexico Basin (Fig. 1). New constraints on the structure of the Baton Rouge fault (BRF) are provided based on high-resolution topographic mapping using LIDAR technology, geodetic leveling, and field observations. LIDAR data show that the BRF is a continuous zone of faults can be traced from the eastern margin of the Mississippi River floodplain to the Pearl River (Fig. 5a). The trace of the fault is continuous along its length except where it crosses active streams where its presence is erased by erosion and/or sedimentation or at relay structures. The fault is marked by an abrupt break in slope whose associated topographic contours are linear and sub-parallel to the fault (Fig. 5b). This is in contrast to the highly fractal patterns of contours typically produced in this low relief, erosion-dominated landscape. Geodetic-quality re-leveling of monuments last occupied in 1994 was performed to test the assumption that the Baton Rouge fault is presently active and to determine its current rate of movement. Three transects were performed east of the Mississippi River and all showed that the south side of the BRF has moved on average ~32-40mm down relative to north side since 1994. An additional transect located just west of the Mississippi River indicates that the fault cuts the Mississippi River. These data indicate that the Baton Rouge fault is currently active and has moved at an average rate of 4-5mm/year between the interval 1994 and 2002.