Eugene Humphreys

Professor of Geophysics
University of Oregon

1272 University of Oregon
Eugene, OR 97403-1272

Cascade 125B
(541) 346-5575
gene@newberry.uoregon.edu

Most of the western U.S. is a broad, uplifted, rugged plateau, and much of this area is currently deforming. Such broadly distributed activity, although relatively unusual, is the process by which most geologic structure is created. The stresses that drive deformation are created by plate interactions and by the high country trying to gravitationally collapse, and these stresses drive shear and extensional deformation. In addition, sinking lithosphere (subducted slab and basal North America lithosphere) drives asthenospheric flow, and this also applies stress on the western U.S. lithosphere. Deformation occurs where lithospheric stress exceeds its strength, and the area that currently is deforming has an inherited low strength, primarily through magmatic heating.

This view of the western U.S. defines most of my research: Where is the buoyancy that holds up the western U.S. and how was it created? How does plate interaction and interaction with the flowing interior of the Earth create the stresses that drive deformation? What processes, tectonic and other, caused the magmatism that heated the weakened lithosphere?

I study these questions with a combination of seismic imaging and geodynamic modeling. For seismic imaging, we use waves from distant earthquakes (teleseisms) to image gross aspects of asthenosphere, lithosphere and crustal structure. These data often are recorded by seismic arrays deployed by my group (frequently in collaboration with other groups). Actual studies are often defined by the interests of individual students.

Seismic imaging. See the following papers (* for student collaborator):

Hales*, Abt*, Humphreys and Roering, Nature, 2005
A lithospheric instability origin for Columbia River flood basalts and Willowa Mountains uplift in northeast Oregon

Schutt* and Humphreys, JGR, 2004
P and S wave velocity and Vp/Vs in the wake of the Yellowstone hotspot, JGR

Humphreys, Hessler*, Dueker, Erslev, Farmer, and Atwater, Int. Geology Review, 2003
How Laramide-age hydration of North America by the Farallon slab controlled subsequent activity in the western U.S.

Crosswhite* and Humphreys, Geology, 2003
Imaging the Mountainless Root of the 1.8 Ga Cheyenne Suture and Clues to its Tectonic Stability

Hammond* and Humphreys, JGR, 2000
Upper mantle seismic wave velocity: The effect of realistic partial melt geometries

Schutt*, Humphreys, and Dueker, Pure and Applied Geophysics, 1998
Anisotropy of the Yellowstone hot spot wake, eastern Snake River Plain, Idaho

Peng* and Humphreys, JGR, 1997
Crustal velocity structure of the eastern Snake River Plain and the Yellowstone swell

Saltzer* and Humphreys, JGR, 1997
Upper mantle P-wave structure of the eastern Snake River Plain and its relationship to geodynamic models of the region

Humphreys and Dueker*, JGR, 1994
Western U.S. upper mantle structure

Geodynamics. See the following papers (* for student collaborator):

Zandt and Humphreys, Geology, 2008
Toroidal mantle flow through the western U.S. slab window

Humphreys and Coblentz, Reviews of Geophysics, 2007
North American dynamics and western U.S. tectonics.

Fay* and Humphreys, Geology, 2006
Dynamics of the Salton block: Absolute fault strength and crust-mantle coupling

Fay* and Humphreys, JGR, 2005
Fault slip rates, effects of elastic heterogeneity on geodetic data, and the strength of the lower crust in the Salton Trough region, southern California

Hammond* and Humphreys, JGR, 2000
Upper mantle seismic wave velocity: The effect of realistic partial melt geometries

Hearn*, and Humphreys, JGR, 1998
Kinematics of the southern Walker Lane Belt and motion of the Sierra Nevada

Hearn*, Humphreys, Chi, and Brown JGR, 1997
The effect of anisotropy on oceanic upper mantle temperatures, structure, and dynamics

Tectonic synthesis. See the following papers (* for student collaborator):

Zandt and Humphreys, Geology, 2008
Toroidal mantle flow through the western U.S. slab window

Hales*, Abt*, Humphreys and Roering, Nature, 2005
A lithospheric instability origin for Columbia River flood basalts and Willowa Mountains uplift in northeast Oregon

Humphreys, Hessler*, Dueker, Erslev, Farmer, and Atwater, Int. Geology Review, 2003
How Laramide-age hydration of North America by the Farallon slab controlled subsequent activity in the western U.S.

Humphreys, Schutt*, Dueker and Smith, GSA Today, 2000
Beneath Yellowstone: Evaluating plume and non-plume models using teleseismic data

Karlstrom and Humphreys, Rocky Mountain Geology, 1998
Persistent influence of Proterozoic accretionary boundaries in the tectonic evolution of southwestern North America: Interaction of cratonic grain and mantle modification events

Humphreys, Geology, 1995
Post-Laramide removal of the Farallon slab, western United States

Humphreys and Weldon, JGR, 1994
Deformation across the western United States: A local estimate of Pacific-North America transform deformation

Humphreys and Dueker*, JGR, 1995
Physical state of the western U.S. upper mantle