SCEC Award Number 14209 View PDF
Proposal Category Collaborative Proposal (Special Fault Study Area)
Proposal Title Measuring Ventura Area Uplift: A Four-Technique Geodetic Study of Vertical Tectonics Combining GPS, InSAR, Leveling and Tide Gauges
Investigator(s)
Name Organization
William Hammond University of Nevada, Reno Reed Burgette New Mexico State University
Other Participants
SCEC Priorities 4a, 1d, 1a SCEC Groups Geodesy, SDOT
Report Due Date 03/15/2015 Date Report Submitted N/A
Project Abstract
 In this study we have combined data from four geodetic techniques to develop a new integrated model of vertical Earth surface motion. These results place new constraints on the elastic strain accumulation in the crust across the faults in the vicinity of the Ventura Basin, a SCEC Special Fault Study (SFSA). We processed large datasets of InSAR, GPS, leveling and tide gauge data to estimate vertical rates over different contemporary time scales. We find rates that vary geographically across the region, with downward rates strongly focused in basins with active groundwater systems and upward motions that are consistent with contractional strain across the thrust faults of the western Transverse Ranges and strike slip San Andreas Fault systems. Agreements of key rates and patterns between the datasets from the different techniques suggest that the features are stable over time on the order of >1 century and are representative of elastic strain accumulation in the interseismic time frame across the region's faults. Thus these signals suggest that GPS and InSAR measure interseismic as well as long-term tectonic uplift related to earthquake cycle deformation and are valuable for constraining slip rates for the Ventura SFSA.
Intellectual Merit Estimates of the rates of the vertical motion of the solid Earth constrain the distribution, rate and style of active strain accumulation in the crust. GPS and InSAR together show that contraction across the active plate boundary fault system, especially across the San Andreas fault system and western Transverse Ranges results in tectonic uplift that is consistent with elastic strain accumulation on buried dislocations, similar to strike slip deformation that is seen in the horizontal GPS data. Thus our results help with understanding the mechanisms by which the crust accommodates strain and mountains are built over geologic time. Additionally the high geographic resolution accessible with the InSAR and leveling analyses improve our ability to separate tectonic and non-tectonic components of the vertical rate field. This project has also resulted in improved methodologies for processing repeated leveling data, which can be applied to other portions of the rich leveling data archive for southern California.
Broader Impacts Modeling performed in another SCEC project (Johnson et al., 2014) has incorporated our results into a model of interseismic strain and slip rates on faults. Our results therefore provide important and complementary constraints on fault slip rates, which are a direct input into the seismic hazard mapping infrastructure of the US Geological Survey. These results stand to have an impact on products that improve the life and safety of the citizens of southern California. Additionally, constraints on vertical motion of the land surface are important for studies of coastal sea level changes because downward crustal motion can cause an increased rate of local sea level rise. This project also provided an early career researcher in the first year of a tenure-track faculty position with a valuable research experience and a chance to interact with the wider SCEC community.
Exemplary Figure Figure 1. Vertical GPS velocities (colored circles with gray outlines) and vertical rates from leveling analysis (colored squares with black outlines) are superimposed on vertical rate inferred from InSAR data. Faults are shown with black lines.

Figure credits: Hammond and Burgette, 2015, SCEC final project report for SCEC Award #14209, Measuring Ventura Area Uplift: A Four-Technique Geodetic Study of Vertical Tectonics Combining GPS, InSAR, Leveling and Tide Gauges.