Subsidence along the Atlantic Coast of the United States: Insights from GPS and late Holocene relative sea level data

Monday, 14 December 2015
Poster Hall (Moscone South)
Makan A. Karegar1, Simon E Engelhart2 and Timothy H Dixon1, (1)University of South Florida Tampa, Tampa, FL, United States, (2)University of Rhode Island, Kingston, RI, United States
Subsidence along the Atlantic coast of the United States is the largest amplitude collapse of a pro-glacial forebulge on Earth. High-quality geological records of late Holocene Relative Sea Level (RSL) are now available for this region. These data provide an independent constraint on Glacial Isostatic Adjustments (GIA), for comparison to continuous GPS measurements that directly measure net vertical crustal motion from GIA and other processes. Installation of more than 130 permanent GPS stations since 2006 represents an improvement towards precise determination of present-day subsidence rates along the coastal plain. We present an improved vertical velocity field for the eastern seaboard of the U.S. and parts of Atlantic Canada with uncertainty estimates that incorporate time-correlated noise.

We use the geologic rates of RSL as an independent constraint to separate the long-term GIA-induced displacement (average motion over past 4 ka) from the GPS vertical displacement (average of one or two decades). Differences between the two are important for mitigating coastal land loss and predicting future storm surge inundation.

Our results indicate that for most areas of the U.S. eastern seaboard there is no difference between GPS rates and late Holocene RSL rates. Exceptions are related to areas of recent excessive groundwater extraction in Virginia and South Carolina. The present-day subsidence rates in these areas are approximately double the long-term geologic rates.