STRUCTURAL CHARACTERISTICS OF ACTIVE NORMAL FAULTS IN SOUTH LOUISIANA: IMPLICATIONS FOR THEIR ORIGIN AND PUBLIC POLICY

Strategies for analysis of active faulting have been developed mainly from studies in arid to semi-arid regions and depend on the creation and preservation of fault-related landforms. South Louisiana’s subtropical climatic conditions, the weak nature of the surface materials cut by faults, and the apparent continuous motion on faults do not promote creation of characteristic landforms. Although normal faults in the region are well known from subsurface studies, and are suspected to be active based on the disruption of built structures, the lack of fault kinematics data has hampered our understanding of mechanics and dynamics of faulting. This has led to misconceptions on the causes of faulting (natural vs. human-induced) and a general lack of awareness of the public safety and property damage hazard posed by the faults. A methodology that combined high-resolution topographic mapping using LIDAR technology, geodetic leveling, analysis of subsurface data, and field observations has been successful in recognizing important characteristics of faults of the region: 1) Active faults are generally not exposed and are marked by fault-line scarps, not surface breaks. Kinematics evidence is thus, essential to prove activity; 2) Current slip rates range from a few mm/yr to over 1 cm/yr; 3) Faults move episodically at time-scales of days to months; 4) Surface deformation associated with faults is limited to areas of hanging wall deformation (roll-overs, and antithetic faults); 5) Stratigraphic analysis suggests that some faults have been active sporadically since the Jurassic. Each period of faulting has coincided with times of sediment loading along the coast. Loading has had the effect of: a) activating long-standing, weak crustal scale faults such as the Tepetate-Baton Rouge system; b) creating a gravitationally unstable mass (Mississippi River delta) that is collapsing under its own weight into the Gulf of Mexico basin and; c) activating the flowage of deep seated salt that promotes faulting.