Observations of Seasonal Deformation Signals in the Yellowstone and Utah GPS

Puskas, Christine; Smith, Robert B.
University of Utah

We present our observations of seasonal signals in the Yellowstone and Wasatch GPS networks. The University of Utah has operated two GPS networks in the Yellowstone-Snake River Plain volcanic system, Idaho-Montana-Wyoming, and the Wasatch Front, Utah, since 1997. Measurements from individual GPS stations over several years reveal notable seasonal variations interpreted to be ground water fluctuations that in turn depend on precipitation, snowpack, and groundwater recharge and discharge rates. Additional factors that may contribute to deformation include pumping, snow loading, atmospheric loading, and lake loading from Yellowstone Lake and the Great Salt Lake. Filtering to separate long-term and short-term deformation indicate that many stations in both networks have a seasonal deformation with maximum peak-to-peak amplitude up to 2 cm in the vertical component and 0.5-1 cm in the horizontal components. In Yellowstone National Park, peak uplift typically occurs in the winter to spring period with maximum subsidence in summer. Peak uplift varies from winter to summer in the Wasatch Front. Various filtering schemes are examined for their effectiveness in extracting the seasonal signals from the GPS data. The filtering schemes are compared with deformation models of fault loading and magmatic deformation in which seasonal motion is obtained from model residuals. The distribution and magnitude of seasonal signals within each network are then analyzed and compared to the distribution of regional aquifers and Quaternary sedimentary basins. The phases of the seasonal signals are compared between stations to determine if there are any systematic variations and are also compared with available streamflow data for possible correlation with surface flow variations.