Assessing Deep-seated Land Subsidence over the Houston Metropolitan area using GPS, Extensometers and InSAR techniques

Land subsidence has caused severe damage to infrastructure in the Houston Metropolitan area, Texas since the 1900s. The subsidence due to extensive groundwater pumping following rapid population growth has been heavily studied during the last two decades. However, the deep-seated subsidence which may relate to deep-seated natural faults needs to be carefully investigated. This research could provide crucial information pertaining to future urban development and a deeper understanding of ongoing faulting and rapid subsidence problems in the Houston metropolitan area. The goal of this study is to explore if deep-seated subsidence is occurring in the Houston-Galveston area. The HoustonNet is a dense GPS network consists of over 210 continuous operating GPS stations installed by the University of Houston and Harris-Galveston Subsidence District since 2013. The majority of HoustonNet GPS stations are located in the rapid subsidence and faulting area. Interferometric synthetic aperture radar (InSAR) has been proved in its ability to monitor ground deformation in high resolution over large coverage. The interferograms derived from ERS-1/2, ENVISAT, and ALOS datasets greatly enhance the spatial coverage for subsidence monitoring. Measurements recorded by HoustonNet GPS stations and 13 borehole extensometers are utilized to investigate the recent subsidence at different depths. The investigation indicates that the recent subsidence (1993-2019) is dominated by the compaction within shallow sediments (< 600 m) including Chicot and Evangeline aquifer in Harris and Galveston County. No measurable compaction was recorded in the Jasper aquifer or its underlying sediments. Deep-seated subsidence is not likely occurring in the Houston-Galveston area. The InSAR results reveal the differential subsiding rates across the major faults in the north of Houston, which indicate the rapid subsidence in northern Houston maybe correlate with active faulting.