An attempt to reconcile subsidence rates determined from various techniques in southern Louisiana

Subsidence rates determined from geodetic releveling observations since 1920 in southern Louisiana are consistently higher than subsidence rates determined from radiocarbon data in the same region over Holocene timescales. Radiocarbon-based subsidence rates are similar to numerically modeled shallow sedimentary compaction rates at similar timescales, while recent geodetic observations are an order of magnitude higher. Possible explanations for the dramatic recent increase in regional subsidence rates suggested by the geodetic data that are considered here include: (I) a recent increase in regional contributions from faulting; (2) the recent contribution of a regional, high-impact process such as fluid withdrawal; (3) accuracy in one or more of the datasets; and (4) a strong dependence of subsidence rates upon the time frame over which different techniques are used. Faulting and regional groundwater withdrawals appear insufficient to explain the high regional geodetic rates. The contribution of regional depressurization from deep fluid withdrawals remains unknown. Estimate errors are likely smaller than the magnitude of the discrepancies between rates from different datasets. Observations of subsidence rates may be biased by measurement duration. (C) 2008 Elsevier Ltd. All rights reserved.