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We have established a stable regional geodetic reference frame using long-history (13.5 years on average) observations from 55 continuously operated Global Navigation Satellite System (GNSS) stations adjacent to the Gulf of Mexico (GOM). The regional reference frame, designated as GOM20, is aligned in origin and scale with the International GNSS Reference Frame 2014 (IGS14). The primary product from this study is the seven-parameters for transforming the Earth-Centered-Earth-Fixed (ECEF) Cartesian coordinates from IGS14 to GOM20. The frame stability of GOM20 is approximately 0.3 mm/year in the horizontal directions and 0.5 mm/year in the vertical direction. The regional reference frame can be confidently used for the time window from the 1990s to 2030 without causing positional errors larger than the accuracy of 24-h static GNSS measurements. Applications of GOM20 in delineating rapid urban subsidence, coastal subsidence and faulting, and sea-level rise are demonstrated in this article. According to this study, subsidence faster than 2 cm/year is ongoing in several major cities in central Mexico, with the most rapid subsidence reaching to 27 cm/year in Mexico City; a large portion of the Texas and Louisiana coasts are subsiding at 3 to 6.5 mm/year; the average sea-level-rise rate (with respect to GOM20) along the Gulf coast is 2.6 mm/year with a 95% confidence interval of ±1 mm/year during the past five decades. GOM20 provides a consistent platform to integrate ground deformational observations from different remote sensing techniques (e.g., GPS, InSAR, LiDAR, UAV-Photogrammetry) and ground surveys (e.g., tide gauge, leveling surveying) into a unified geodetic reference frame and enables multidisciplinary and cross-disciplinary research.

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Data obtained by GRACE (Gravity Recovery and Climate Experiment) have been used to invert for the seismic source parameters of megathrust earthquakes under the assumption of either uniform slip over an entire fault or a point‐like seismic source. Herein, we further extend the inversion of GRACE long‐wavelength gravity changes to heterogeneous slip distributions during the 2011 Tohoku earthquake using three fault models: (I) a constant‐strike and constant‐dip fault, (II) a variable dip fault, and (III) a realistically varying strike fault. By removing the post‐seismic signal from the time series, and taking the effect of ocean water redistribution into account, we invert for slip models I, II, and III using co‐seismic gravity changes measured by GRACE, de‐striped by DDK3 decorrelation filter. The total seismic moments of our slip models, with respective values of 4.9×1022 Nm, 5.1×1022 Nm, and 5.0×1022 Nm, are smaller than those obtained by other studies relying on GRACE data. The resulting centroids are also located at greater depths (20 km, 19.8 km, and 17.4 km, respectively). By combining onshore GPS, GPS‐Acoustic, and GRACE data, we obtain a jointly inverted slip model with a seismic moment of 4.8×1022 Nm, which is larger than the seismic moment obtained using only the GPS displacements. We show that the slip inverted from low degree space‐borne gravimetric data, which contains information at the ocean region, is affected by the strike of the arcuate trench. The space‐borne gravimetric data help us constrain the source parameters of a megathrust earthquake within the frame of heterogeneous slip models.