Subsidence and Fault Displacements Along the Long-Point Fault Derived from Continuous GPS Observations (2013-2017)

The Long-Point Fault located in Houston, Texas is part of a complex system of normal growth faults along the Texas Gulf Coast that repeatedly causes damage to infrastructure on both private and public property. This study uses Continuously Operating Reference GPS Stations (CORS) to delineate the fault motions along the Long-Point Fault and its interaction with subsidence from 2013 to 2017. Fault displacements were determined with eleven GPS stations installed along both sides of the fault. On the hanging-wall side of the fault there are six CORS stations and on the footwall side there are five CORS stations installed. GPS processing methods used include relative (double difference) and absolute positioning known as Precise Point Positioning (PPP). PPP solutions are referenced to a global reference frame (IGS08) that were then transformed into the local Stable Houston Reference Frame 2016 (SHRF16). At this time, the Long-Point Fault shows no considerable displacement between the hanging wall and the footwall and can be considered inactive. Within the SHRF16 both sides of the Long-Point Fault are moving horizontally to the northwest at a rate of ~ 0.4 cm/year and subsiding at a rate of ~0.9 cm/year. These horizontal motions to the northwest are likely attributed to the subsidence bowl observed in the Jersey Village area. Furthermore, groundwater potentiometric levels appear to have a direct impact on surface elevation; as groundwater levels rise and fall the surface rises and falls. Areas where groundwater levels have not recovered to preconsolidation elevation experience higher rates of subsidence than areas where the preconsolidation head has been restored. The integrated GPS, groundwater, and precipitation observations provide new insight on how variability of groundwater, and subsidence effect fault displacement.