GPS Imaging of vertical land motion in California and Nevada: Implications for Sierra Nevada uplift

• Published in: Journal of geophysical research. Solid earth Vol. 121; no. 10; pp. 7681 - 7703
• Main Authors: Hammond, William C., Blewitt, Geoffrey, Kreemer, Corné
• Format: Journal Article
• Language: English
• Published: United States 01.10.2016
• Subjects: crustal loading; geodesy; groundwater; mountain uplift; plate boundary zone; tectonics; crustal loading; mountain uplift; groundwater; plate boundary zone; tectonics; geodesy
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1002/2016JB013458

We introduce Global Positioning System (GPS) Imaging, a new technique for robust estimation of the vertical velocity field of the Earth's surface, and apply it to the Sierra Nevada Mountain range in the western United States. Starting with vertical position time series from Global Positioning System (GPS) stations, we first estimate vertical velocities using the MIDAS robust trend estimator, which is insensitive to undocumented steps, outliers, seasonality, and heteroscedasticity. Using the Delaunay triangulation of station locations, we then apply a weighted median spatial filter to remove velocity outliers and enhance signals common to multiple stations. Finally, we interpolate the data using weighted median estimation on a grid. The resulting velocity field is temporally and spatially robust and edges in the field remain sharp. Results from data spanning 5–20 years show that the Sierra Nevada is the most rapid and extensive uplift feature in the western United States, rising up to 2 mm/yr along most of the range. The uplift is juxtaposed against domains of subsidence attributable to groundwater withdrawal in California's Central Valley. The uplift boundary is consistently stationary, although uplift is faster over the 2011–2016 period of drought. Uplift patterns are consistent with groundwater extraction and concomitant elastic bedrock uplift, plus slower background tectonic uplift. A discontinuity in the velocity field across the southeastern edge of the Sierra Nevada reveals a contrast in lithospheric strength, suggesting a relationship between late Cenozoic uplift of the southern Sierra Nevada and evolution of the southern Walker Lane. Plain Language Summary Mountain growth attributable to the steady action of plate tectonics is difficult to observe directly because it is extremely slow. We developed a new method called GPS Imaging to combine and filter large datasets of high precision GPS data that have been collected for many years in California and Nevada. We use the method to generate new informative images of the workings of the uplift of Sierra Nevada Mountains, earthquake cycle deformation, and regional subsidence attributable to groundwater withdrawal. The Sierra Nevada experiences uplift of up to 2 mm/yr (about 8 inches per century), and that uplift is faster in more recent years confirming that some of it is a response to climate change and human controlled pumping of groundwater that intensified during the drought of 2012–2015. The images also reveal a break in the Earth's plate, separating the Sierra Nevada from the Great Basin, and allowing the Sierra crest to rise more quickly. Key Points GPS Imaging is a new technique that provides a temporally and spatially robust vertical velocity field for geodynamic studies The Sierra Nevada is the most rapid and extensive uplift feature in the western United States, rising up to 2 mm/yr Images of an uplift discontinuity suggest that current rise of the Sierra Nevada is associated with evolution of the southern Walker Lane