GPS AND INSAR INTEGRATED FAULTING, SUBSIDENCE, AND SEASONAL GROUND DEFORMATION MONITORING IN HOUSTON, TEXAS, USA

For approximately 100 years, the Houston region has been adversely impacted by ground movements associated with active faulting, subsidence, and seasonal ground deformation, which have caused costly recurring damages to private and public infrastructure, including buildings, roadways, parking lots, and utility lines. The rapidly growing population in the Houston region means that the ongoing ground movements must be vigilantly monitored. In this study, we have introduced detailed methods using GPS, InSAR, and GPS-enhanced InSAR (GInSAR) to monitor faulting, subsidence, and seasonal ground deformation. The Houston region has numerous gravitationally induced “down-to-the-coast” growth faults that represent slow sliding of the land mass towards the Gulf of Mexico. The Long Point Fault is one of those active urban faults belonging to the complex normal fault system. We use a GPS array with 12 permanent stations installed along the two sides of the 16-km-long fault scarp to assess the activity of the Long Point Fault. The six-year continuous GPS observations (2013-2018) indicate that the Long Point Fault is currently inactive, with the rates of dip-slip and strike-slip being below 1 mm/year. GInSAR-derived subsidence rates (2015-2019) also suggest no considerable differences between the hanging wall and footwall sides along the Long Point Fault. Current surficial damages in the Long Point Fault area are more likely caused by ongoing uneven subsidence (~ 1 cm/year) and its induced horizontal strains, as well as the significant seasonal subsidence and heave, rather than deep-seated or tectonic-controlled fault movements. For mapping both the long-term (multiple years) and short-term (inter-annual. Seasonal) subsidence in the Houston region, we use the GInSAR method, integrating GPS and Sentinel-1A InSAR datasets covering the entire Houston region from 2015 to 2019. The root-mean-square (RMS) of the detrended InSAR-displacement time series is able to achieve a level of sub-centimeter accuracy, and the uncertainty (95% confidence interval) of the InSAR-derived subsidence rates is able to achieve a couple of millimeters accuracy per year for 5-year or longer datasets. The GInSAR mapping results suggest moderate ongoing subsidence (~ 1 cm/year) in northern Waller County, western Liberty County, and the city of Mont Belvieu in Champers County, which were not recognized in previous GPS-based investigations; the GInSAR mapping results also suggest that previous investigations overestimated the ongoing subsidence in western Montgomery County. This study indicates that hydraulic-head changes in the Evangeline aquifer are the primary cause of ongoing long-term and seasonal subsidence in the Houston region. The former is dominated by inelastic deformation, and the latter is dominated by elastic deformation. Both could cause infrastructure damage. This study demonstrated the potential of employing the GInSAR methods for near-real-time subsidence monitoring in the greater Houston region. The near-real-time monitoring would also provide timely information for understanding the dynamic of groundwater storage and improving both long-term and short-term groundwater resource management.