Subcontinental-Scale Crustal Velocity Changes Along the Pacific-North America Transform Plate Boundary From BARGEN GPS Data
Full citation: Davis, J. L., Wernicke, B.L., Bisnath S., Niemi, N. A., and Elósegui, P. (2006) Subcontinental-Scale Crustal Velocity Changes Along the Pacific-North America Transform Plate Boundary From BARGEN GPS Data, Nature, 441, 1131 doi:10.1038/nature0478112/2006
Abstract
Transient tectonic deformation has long been noted within
∼100 km of plate boundary fault zones and within active volcanic
regions, but it is unknown whether transient motions also occur at
larger scales within plates. Relatively localized transients are
known to occur as both seismic and episodic aseismic events,
and are generally ascribed to motions of magma bodies, aseismic
creep on faults, or elastic or viscoelastic effects associated with
earthquakes. However, triggering phenomena and systematic
patterns of seismic strain release at subcontinental (∼1,000 km)
scale along diffuse plate boundaries have long suggested that
energy transfer occurs at larger scale. Such transfer appears to
occur by the interaction of stresses induced by surface wave
propagation and magma or groundwater in the crust, or from
large-scale stress diffusion within the oceanic mantle in the
decades following clusters of great earthquakes. Here we report
geodetic evidence for a coherent, subcontinental-scale change in
tectonic velocity along a diffuse ∼1,000-km-wide deformation
zone. Our observations are derived from continuous GPS (Global
Positioning System) data collected over the past decade across the
Basin and Range province, which absorbs approximately 25 per
cent of PacificÐNorth America relative plate motion. The observed
changes in site velocity define a sharp boundary near the centre of
the province oriented roughly parallel to the north-northwest
relative plate motion vector.We show that sites to the west of this
boundary slowed relative to sites east of it by,∼1mmyr–1 starting in late 1999.
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Acknowledgements: This work was supported by the National Science
Foundation and the US Department of Energy. UNAVCO, Inc., supports
BARGEN site implementation, operation and maintenance. The authors thank
R. Bürgmann for comments on the manuscript.
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