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Wayne Thatcher
Abstract: Rheological Stratification of the Lithosphere:
Constraints from Space Geodesy
Postseismic transient deformation, isostatic rebound from removal of pluvial lake loads, and lithospheric deflection due to reservoir impoundment are each converging on consistent rheological models for the crust and upper mantle of the western United States. These results imply a strong elastic crust 25-40 km thick overlain by a viscoelastic substrate with an effective viscosity of ~1018 to 1019 Pas. Results are obtained from:
- Deformation imaged by InSAR and GPS following the 1992 Landers and 1999 Hector Mine, California earthquakes;
- Leveling surveys following the 1959 M=7.3 Hegben Lake, Montana earthquake;
- Isostatic rebound of Lake Bonneville, Utah;
- Leveling surveys following filling of Lake Mead, Arizona in 1935.
The most surprising result of these studies is that the upper mantle is weaker than the lower crust. However, the lower crust in these regions may deform by ductile flow and the data provide a lower bound of ~10 20 Pas for its effective viscosity.
Wayne Thatcher, U. S. Geological Survey
Brief Professional Bio
I am a Research Geophysicist with the U. Geological Survey in Menlo Park California. My research applies space geodetic measurements of Earth’s surface movements around active faults and volcanoes to understand the processes that lead to earthquakes and eruptions. Satellite geodesy is revolutionizing our ability to map surface movements in space and time. Global Positioning System (GPS) measurements permit us to make point measurements at critical locations, either using periodic surveys or continuously at permanent sites. Interferometric Synthetic Aperture Radar (InSAR) techniques provide complete spatial mappings of deformation over time intervals of months or years. Our group is actively applying these methods to view how the interior western U.S. is deforming and to image the patterns of ground movements around volcanoes, both when eruptions appear imminent and when volcanoes are apparently quiescent. Using the observed movements we construct models of the sources of deformation. We integrate geodetic data and models with results from active process geology, geomorphology, seismology and geophysics to better understand the physics of earthquake faulting and volcanism.
My research is funded by the USGS’s Earthquake Hazard Reduction Program, the Volcano Hazards Program, and NASA’s Solid Earth and Natural Hazards Program.
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