A stable reference frame for the study of ground deformation in the Houston metropolitan area, Texas

A great number of GPS stations have been installed in the Houston, Texas area for studying ground deformation caused by subsidence, salt dome uplift, and fault creep. One major consideration in determining the magnitude and velocity of ground displacement over time using GPS, particularly for horizontal ground deformations, is the selection of reference frames. In this study, we define a Stable Houston Reference Frame (SHRF) using over 8-year of continuous data from 10 permanent GPS stations. These stations are located throughout Harries County and nearby counties, and cover an area of about 200,000 km 2 . The realization of SHRF is defined in terms of a Helmert transformation from the International GNSS (Global Navigation Satellite System) Reference Frame of 2008 (IGS08). SHRF is aligned with the IGS08 at epoch 2012.0. The velocities of these 10 frame stations are minimized to zero within the stable reference frame. The GIPSY/OASIS (V6.1.2) software package was used to calculate position coordinates within IGS08. The precise point positioning (PPP) daily solutions within SHRF achieve 2-3 mm horizontal accuracy and 6-7 mm vertical accuracy. The main results of this article include (1) accurate global (IGS08) positions and velocities of 10 selected frame sites, and (2) 14 parameters for reference frame transformation from IGS08 to SHRF. SHRF will be incrementally improved and be synchronized with the update of IGS reference frame.