Nevada Bureau of Mines and Geology
University of Nevada, Reno
Reno, Nevada 89557-0178, USA
Office location: Scrugham Engineering/ Mines, Room 315
Office Phone: 1 (775) 784-6436
Fax: 1 (775) 784-1709
Email Bill
For Publication list and .pdf files see:
Bill's Curriculum Vitae
The mountains of the Basin and Range are largely created in response to slow distributed province-wide extension that breaks the Earth's crust along fault zones. Cumulative displacement along these faults over long periods of time builds topographic relief, i.e. the valleys and ranges of the province. Earthquakes associated with the infrequent slip on these faults generate seismicity that is often felt by people who live in the growing population in the Great Basin.
In my research I precisely measure this active crustal deformation using geodetic techniques such as the Global Positioning System (GPS). From these measurements I infer the style and distribution of Earth surface deformation that is a direct consequence of continent-scale tectonic processes. My main interest is in relating these motions to the organization of seismogenic faulting, and inferring the source of stresses in the lithosphere. With GPS we can better understand the processes that control gradual deformation of the western U.S. continental interior, and hence better understand the physics of Earth deformation and the source of potentially damaging earthquakes.
The forces that drive these lithospheric-scale motions are attributed to 1) interactions between the North American, Pacific and Juan de Fuca plates, and 2) internally generated gravitational forces that cause the high-elevation interior to slowly collapse, and 3) tractions at the base of the lithosphere that resist or drive deformation. Modeling of lithospheric-scale deformation helps me to distinguish between these different causes and to infer how stresses are transmitted large distances from the plate boundary, causing active deformation of the western U.S. interior."
Kreemer and Hammond (2007) using geodetic velocities we looked at the present-day areal changes in the Pacific-North America plate boundary zone and we build a case for a kinematic link between extension in the Basin and Range and crustal shortening in northern California above the southern most Cascade subduction zone. This idea is backed up by independent geodynamic indicators and enforces the idea that the southern Cascade subduction zone may act as a 'window escape' for the Basin and Range material to flow/collapse towards.
Also see This Link for a related Research Focus article by Lucy Flesch.
Hammond and Thatcher, (2004) measured tectonic deformation across the Basin and Range province near the latitude of Reno, Lake Tahoe and Wasatch Front. Surveying this ~800 km long network with campaign GPS revealed concentrations of deformation at the eastern and western extremes of the province, and improved our understanding of the broad-scale patterns of deformation across the western United States.
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mmond and Thatcher, (2005) used campaign and continuous GPS measurments to infer the pattern of deformation in the northwestern quadrant of the Basin and Range province. These results show that this region is actively deformed by San Andreas-parallel dextral shear, intracontinental extension, contraction associated with Cascadia interseismic deformation, and contraction associated with the northwestward impingment of the Sierra Nevada microplate into Cascadia.
Hammond and Thatcher, (2007) (paper in press at JGR) used new campaign GPS measurements and data existing in the GPS data archives to assimilate the observations into a block model of interseismic deformation in the western Basin and Range province. The results show that although the strain maps of Kreemer et al. 2005 show a pattern of monotonically increasing strain to the western boundary of the province, fault slip rates may not monotonically increase westward. A correction for CNSB postseismic deformation is applied and a new block modeling formulation is presented.
Hammond, Kreemer, Blewitt, (2007) (paper in review) used a new compilation of campaign and continuous GPS measurements of Basin and Range and Sierra Nevada motions and seismic data to infer the viscoelastic properties of the upper mantle and lower crust in central Nevada. They showed that the effects of earthquakes that occured decades ago can have large effects on the contemporary GPS velocity field in the Great Basin. Their model allows them to predict the effects of Central Nevada Seismic Belt relaxation on the horizontal GPS velocity field and hence correct for these seismic cycle effects.
Hammond (2005) discusses the implications of postseismic viscoelastic relaxation of the upper mantle beneath the Central Nevada Seismic Belt following the 20th centure earthquakes that occured there. In particular the effect on geodetic measurments of horizontal motions associated with strain accumulation on faults in the western U.S. are discussed. This persepctive article for Science magazine accompanies the article by Gourmelen and Amelung, 2005, that used Interferometric Synthetic Aperture Radar (InSAR) to detect the vertical motions associated with this phenomenon.
Hammond and Plag (2007) use public domain GPS data to quantify the vertical land motion that contributes to sea level rise in the vicinity of Venice Italy. Special consideration is given to the evaluation of the uncertainties in vertical motion, which is subject to inaccuracies and uncertainties in the global reference frame's connection to the Earth's center of mass. The results of this work have been used to evaluate future scenarios for sea level rise for the Island of Venice (Plag et al., 2005).