Liu, and seven co-authors, reported in 2019 that the Long Point Fault is one of the most active urban faults in Houston, Texas, which belong to a complex system of normal growth faults along the Texas Gulf Coast. To assess the activity of the Long Point Fault, a GPS array with 12 permanent stations was installed along the two sides of the known 16-km-long fault scarp in 2013. GPS datasets were processed with the Precise Point Positioning (PPP) and Double-Difference (DD) methods. The daily PPP solutions with respect to the International Global Navigation Satellite System (GNSS) Reference Frame 2014 (IGS14) were converted to the Stable Houston Reference Frame (Houston16).
The six-year continuous GPS observations indicate that the Long Point Fault is currently inactive, with the rates of down-dip-slip and along-strike-slip being below 1 mm/year. The Long Point Fault area is experiencing moderate subsidence varying from 5 to 11 mm/year and a coherent horizontal movement towards the northwest at a rate of approximately 2 to 4 mm/year. The horizontal movement is induced by the subsidence bowl that has been developing since the 1980s in the Jersey Village area. Current surficial damages in the Long Point Fault area are more likely caused by ongoing uneven subsidence and its induced horizontal strains, as well as the significant seasonal ground deformation, rather than deep-seated or tectonic-controlled fault movements. The results from this study suggest a cause-and-effect relationship between groundwater withdrawals and local faulting, which is pertinent to plans for future urban development, use of groundwater resources, and minimization of urban geological hazards.
The Houston metropolitan area, more broadly the Gulf Coast region, has numerous gravitationally induced “down-to-the-coast” faults that represent slow sliding of the land mass towards the Gulf of Mexico. Some of these faults have resulted in costly damages to private and public surface infrastructure including buildings, roadways, parking lots, drainage structures, utility systems, and building foundations. The damages require constant repairs that burden private citizens, businesses, and government agencies. Active faults in Houston were first recognized as early as 1926. By 1973, about 52 historically active faults had been recognized in the Houston area with an aggregate length of 220 km. By 1979, the number of identified historically active faults had increased to over 150 and the total length was over 500 km [6–8]. Recently, more urban faults have been identified based on high-resolution digital elevation models (DEMs) derived from airborne Light Detection and Ranging (LiDAR) and Interferometric Synthetic Aperture Radar (InSAR) datasets in the Houston metropolitan area [9–11]. Figure 1 illustrates the principal faults in the Houston metropolitan area mapped by the US Geological Survey (USGS) using high-resolution airborne LiDAR data collected in October 2001 [12]. These faults have been documented at depths from 1000 to 4000 m based on extensive investigations using geophysical well logs and deep seismic surveys. The growth fault systems that cut the Pre-Miocene-age sediments (Holocene-, Pleistocene-, and Pliocene-age sediments) were formed millions of years ago during the formation of the Gulf of Mexico [8].
Previous studies reported that many of the Houston faults moved on average at downward rates of 0.5 to 3 cm/year during the periods that they studied. These investigations also realized the variations of the movements of Houston faults in space and time. Verbeek et al. out that the movements of many Houston faults were episodic. Sections of some faults that had been dormant for years could suddenly become active, as illustrated dramatically by the fault at Goose Creek oil field. Conversely, other faults with a long history of damage to man-made structures may become inactive. No significant earthquakes have occurred on these faults in historic times, but recurring infrastructure damages have been frequently observed in the vicinity of the fault areas since the 1960s. citizens, businesses, and government agencies.
For a comprehensive review of subsidence and faulting in the Houston, Texas area, see: Campbell, et al., (2018): http://www.i2mconsultants.com/downloads/corp/JGG-1-015.pdf
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