Deformation Along the Rio Grande Rift: Investigating the Spatial and Temporal Distribution of Strain Using GPS

Abstract:

Low velocity (<1 mm/yr) extensional environments, such as the Rio Grande rift (RGR) in Colorado and New Mexico, are complex but can provide insights into continental dynamics, tectonic processes, and seismic hazards. We use eight years of measurements from 26 continuous GPS stations across the RGR installed as part of a collaborative EarthScope experiment. We combine this data with regional Plate Boundary Observatory (PBO) and National Geodetic Survey (NGS) CORS GPS stations, and survey-mode data collected on NGS benchmarks to investigate how deformation is distributed across a broad area from the Great Plains to the Colorado Plateau. The data from over 150 stations are processed using GAMIT/GLOBK, and time series, velocities, strain rates are estimated with respect to realizations of a stable North America reference frame, such as NA12. This study extends our previous analysis, based on 4 years of data, which found an approximately uniform 1.2 nanostrain/yr east-west extensional strain rate across the entire region that was not concentrated on the narrow surface expression of the rift. We expand on this previous work by using a denser network of GPS stations and analyzing longer time series, which reduce horizontal velocity uncertainties to approximately 0.15 mm/yr. We also improve the accuracy of the estimated velocity uncertainties by robustly characterizing time-correlated noise. The noise models indicate that both power-law and flicker noise are present in the time series along with white noise. On average, power law noise constitutes about 90% of the total noise in the vertical component and 60% in the horizontal components for the RGR sites. We use the time series, and velocity and strain-rate estimates to constrain spatial and temporal variations in the deformation field in order to locate possible regions of strain localization and detect transient deformation signals, and to address some of the kinematic and dynamic issues raised by the observation that a broad, low seismic velocity zone underlies the narrow geologic surface expression of the RGR defined by normal fault bounded basins.