QUANTIFYING LATE QUATERNARY FAULT MOVEMENT IN THE TEPETATE-BATON ROUGE FAULT ZONE SOUTHEAST LOUISIANA: IMPLICATIONS FOR COASTAL SUBSIDENCE

There are considerable concerns about faulting as a major driver of regional subsidence in southeast Louisiana, although measurements of rates of fault movement are rare. The Tepetate-Baton Rouge fault zone (TBRFZ) is morphologically the most prominent fault system along the northern Gulf of Mexico coast with known recent activity. Previous studies have pinpointed the TBRFZ as a major boundary between the “stable” North American continent and a rapidly subsiding coastal zone. Here we present throw rate data from 11 fault segments within the TBRFZ, measured over time scales spanning the last interglacial to the late Holocene. Throw rates averaged over the late Pleistocene to present are 0.03-0.04 mm/yr and are spatially uniform, probably related to aseismic motion of weakly interacting gravity-driven faults within the fault zone. The late Holocene mean throw rate is ~0.22 mm/yr, i.e., larger than the late Pleistocene rates. We attribute this acceleration to the rapid accumulation of Holocene sediment proximal to the fault zone. Nevertheless, the late Holocene throw rate is up to two orders of magnitude smaller than the rates of land-surface subsidence in the Mississippi Delta, indicating that the TBRFZ is not a dominant contributor to subsidence in this region.