Funds from this Small Grant for Exploratory Research (SGER) support a collaborative effort by PIs Tim Dixon (Miami - RSMAS) and Roy Dokka (LSU) to conduct GPS resurveys of existing campaign benchmarks in the New Orleans area and to establish 10 additional continuously operated and permanently monumented GPS stations in the region. The recent tragic flooding of New Orleans, Louisiana, associated with Hurricane Katrina on August 29, 2005, emphasizes the hazardous setting of this urban area. Preliminary GPS and leveling data collected by the PIs suggest that New Orleans is subsiding rapidly because it is located in the hanging wall of an active listric normal fault system (the Michoud fault) that accommodates southward motion of the Mississippi delta into the Gulf of Mexico. Averaged over the last decade, southward motion of this upper crustal block relative to the stable interior of North America occurs at a rate of 2.3 plus or minus 1.7 mm/yr. Leveling data suggest that the rate of motion may have been higher in the recent past. The average subsidence rate for GPS sites located on the delta is 5.2 plus or minus 2.3 mm/yr relative to Earths's center of mass, or about 7 mm/yr relative to mean sea level. Movement of the delta block on the listric fault appear to be facilitated by underlying salt horizons that have been imaged by seismic reflection campaigns. These horizons accommodate deformation via ductile flow at low temperatures, hence there is little or no seismicity associated with faulting. The proposed additional GPS observations will help to confirm the proposed Michoud fault dynamics and to test the possibility that ground deformation accelerated following Katrina-related water mass loading. Data from this project will provide critical background tectonic framework to guide policy makers during the rebuilding of New Orleans.
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