The Maximum Compaction Depth of the Aquifers in the Houston-Galveston Area: a result from long-term GPS and extensometer observations

Abstract:

This study investigated the recent subsidence observed at different depths in the Houston-Galveston area. The subsidence was recorded by using 13 borehole extensometers and 76 GPS antennas. Four of the GPS antennas are mounted on the deep-anchored (549, 591, 661 and 936 m below the land surface) inner pipes of borehole extensometers. They are located at approximately the same depth as the bottom of Evangeline aquifer. There are two pairs of closely-spaced ( about 100 m) extensometers. They were completed at different depths and show the variation of compaction rate in depth. We conclude that recent subsidence (1993-2012) in the Houston-Galveston area was dominated by the compaction of sediments within 600 m below the land surface. Deep-anchored GPS data shows stable vertical movement indicating no measurable compaction at the depth of the Jasper aquifer or within deeper strata. Depending on the location of specific sites, the compaction could occur from a depth as shallow as that within the Chicot aquifer to the maximum depth at the middle of the Evangeline aquifer.