The Ups and Downs of Southern California: Mountain Building, Sea Level Rise, and Earthquake Potential from Geodetic Imaging of Vertical Crustal Motion

William C. Hammond, Geoffrey Blewitt, Corné W. Kreemer, Reed J. Burgette, Kaj M. Johnson, Charles M. Meertens, & Frances Boler

Submitted September 20, 2016, SCEC Contribution #6402, 2016 SCEC Annual Meeting Talk on 9/13 10:30 (PDF)

Contemporary tectonic uplift in California and Nevada is an active part of ongoing plate boundary processes driving earthquakes. However, it has so far been difficult to confidently resolve and interpret uplift patterns. The challenges are twofold. First is the geodetic problem of isolating the signal of crustal-scale vertical motion given a large number of noisy time series from multiple networks irregularly distributed in space and time. Second is the problem of partitioning the signals into patterns of long-term tectonic deformation, earthquake cycle, flexural/isostatic adjustment, local basin response from groundwater hydrology, crustal loading, and/or mantle flow.

The spread of precise GPS networks and new developments in processing GPS data are leading to a clearer and more complete picture of vertical motions, improving knowledge of the rates of mountain growth, associated fault slip, and seismic hazard. To address the explosion in the quantity of new measurements, the ‘Plug and Play’ initiative is easing access to these data for everyone, enhancing their utility and impact. Plug and Play removes barriers at the beginning and end of the GPS processing chain, providing a free GPS data processing service and back-end products with free and open access. Currently the system has global scope, providing products for ~15,000 stations. To derive uplift maps from the data we apply our new robust estimation method "GPS Imaging" that combines non-parametric robust trend estimation with median-based despeckling and spatial filtering to suppress noise.

The resulting images show that the Sierra Nevada is the most rapid and extensive uplift feature in the western United States, rising up to 2 mm/yr, with uplift strongly modulated by climatic and anthropogenic forcing from groundwater pumping. The images reveal a discontinuity in the uplift field across Owens’ Valley, suggesting that Sierra Nevada uplift is associated with crustal extension in the southern Walker Lane. Across the Western Transverse Ranges (WTR) of southern California we have taken the analysis further by combining four geodetic techniques: GPS, InSAR, levelling and tide gauges to constrain the vertical rate field. These results reveal 1-2 mm/yr of uplift across the WTR and San Gabriel Mountains block, focused west of the San Andreas fault, consistent with upward interseismic extrusion of these blocks as they experience contraction against the San Andreas Fault.

Key Words
Tectonic geodesy, strain accumulation, uplift, subsidence, GPS, InSAR, Tige Gauges, Levelling

Hammond, W. C., Blewitt, G., Kreemer, C. W., Burgette, R. J., Johnson, K. M., Meertens, C. M., & Boler, F. (2016, 09). The Ups and Downs of Southern California: Mountain Building, Sea Level Rise, and Earthquake Potential from Geodetic Imaging of Vertical Crustal Motion. Oral Presentation at 2016 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy