Regional and Local Subsidence in Louisiana

摘要

The measurement of local, man-induced subsidence is especially critical in areas with high rates of land loss. To measure this subsidence, absolute historical geodetic movements have been estimated by adjusting all movements along the first-order vertical control network from northeast to southwest Louisiana as related to the Monroe uplift. The adjustment will serve as a base line by which local subsidence or uplift can be measured. A generalized trend of increasing subsidence to the south in Louisiana probably reflects increasing sediment thickness and weight toward the axis of the Gulf Coast basin. Anomalous values as low as -17.6 mm/y (-0.7 in./y) occur in areas overlying Pleistocene and Holocene fluvial elements. Positive movement as high as +4.1 mm/y (+0.2 in./y), has been found to be associated with the Iberian structural axis in south-central Louisiana. Land subsidence due to natural causes may far outweigh subsidence resulting from fluid withdrawal or depressurization of geopressured aquifers. The effects of regional and local natural processes should not be underestimated in any systematic approach to measuring subsidence. (ERA citation 09:043186)