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This project uses the familiar GPS satellites together with scientific InSAR satellites to measure with millimeter precision the vertical movement of the Sierra Nevada mountain range and Great Basin in the region spanning the border between California and Nevada. Initial results from the first funded phase of the project show that the Sierra Nevada are moving upward at a surprisingly fast rate of about 1 millimeter per year relative to the Great Basin. The upward movement appears to be that of a solid block with little internal deformation, though this requires testing with more detailed measurements and modeling. In contrast, the Great Basin itself is known to be very geologically active, with frequent earthquakes up to large magnitudes, and with measurable east-west extension. Yet, after accounting for models of earthquakes over the last century, the Great Basin does not appear to move up or down relative to the center of the Earth to within the margins of error. Therefore the project's initial results indicate that the Sierra Nevada are actually uplifting relative to the center of the Earth. It would therefore appear that the Sierra Nevada are undergoing a modern spurt of geological activity, and have grown to their present height relatively quickly in the last few million years. The goal of this project is to shed more light as to whether this is indeed the case, and if so, how can it be explained.
Now that these initial results are published, the objective of this project now is to refine the precision and coverage of these satellite-based measurements to get a more accurate and detailed map of how fast the Earth's surface is moving up and down in the study region. Enhanced precision and detail are allowing for more advanced modeling of the various processes that may be associated with vertical movement, that should lead to a stronger understanding of what may be driving contemporary uplift in the Sierra Nevada. The measurements are being enhanced by extending the observational period by another 4 years, by adding more GPS coverage to the analysis, including new stations recently installed by this project, and by extending the coverage of scenes from InSAR satellite data. The reference system that enables us to locate the center of mass of the Earth continues to be improved. This development continues to reduce the error in determining the absolute uplift rate of the Sierra Nevada. Moreover, together with improved models of how the Earth deforms following large earthquakes in the Great Basin, this may allow us to detect whether the Great Basin is moving up or down with respect to the Earth's gravity field, which has implications as to the Great Basin's history and how it is evolving today, and therefore how this might influence the evolution of the Sierra Nevada.
This project has the broader goal of addressing a long-standing controversy about the history and mechanisms behind uplift of the Sierra Nevada, with the age of modern topography estimated (prior to this project) between 3 to 60 million years old, with our project favoring the earlier scenario. If the results hold up, they will help to constrain models the evolution of the Great Basin, as it is known from geological analysis of ancient canyons that the western flank must at some point have gravitationally collapsed to become the modern Great Basin. Understanding uplift and collapse of this system is thus important from many perspectives, including the past and future evolution of the plate boundary between North America and the Pacific, the stresses on active faults today (including the San Andreas Fault), and explaining the variation in style of strain and faulting across this seismically active region. Thus the project feeds into a broader program of understanding when and where earthquakes are likely to occur, and help inform prepare citizens on seismic hazards. Another broader benefit of this project is that the Earth's surface also moves up and down from the presence of water in the ground. Thus data from this project is also being used to explore its utility in improving large-scale models of hydrology in this largely arid region, to help address challenges in managing and sustaining water resources.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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Blewitt, G., C. Kreemer, W.C. Hammond, and J.M. Goldfarb. "Terrestrial reference frame NA12 for crustal deformation studies in North America," Journal of Geodynamics, v.72, 2013, p. 11.
Amos, C.B., P. Audet, W.C. Hammond, R. Burgmann, R., I.A. Johanson, and G. Blewitt. "Uplift and seismicity driven by groundwater depletion in central California," Nature, v.509, 2014, p. 483-486.
Blewitt, G., C. Kreemer, W.C. Hammond, and J.M. Goldfarb. "Terrestrial reference frame NA12 for crustal deformation studies in North America," Journal of Geodynamics, v.72, 2013, p. 11-24.
Kreemer, C. W., Blewitt, G., Klein, E. C.. "A geodetic plate motion and global strain rate model," Geochemistry, Geophysics, Geosystems, v.15, 2014, p. 3849-3889.
Hammond, W. C., Blewitt, G., Kreemer, C. W.. "Steady contemporary deformation of the central Basin and Range province, western United States," Journal of Geophysical Research, v.119, 2014, p. 5235-5253.