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Subcontinental-scale crustal velocity changes along the Pacific–North America plate boundary


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 events1, and are generally ascribed to motions of magma bodies, aseismic creep on faults, or elastic or viscoelastic effects associated with earthquakes. However, triggering phenomena2,3 and systematic patterns of seismic strain release at subcontinental (1,000 km) scale along diffuse plate boundaries4,5 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 crust6, or from large-scale stress diffusion within the oceanic mantle in the decades following clusters of great earthquakes7. 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 Pacific–North 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 1 mm yr-1 starting in late 1999.

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Figure 1: Sites of the northern BARGEN GPS network.
Figure 2: Illustration of the post-analysis procedure, using time series of east position for four BARGEN sites.
Figure 3: Analysis of spatial variation of nonlinear deviations.
Figure 4: Differences of horizontal velocity for one-year periods relative to the average velocities for the period 1997.0–2002.0.


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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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Correspondence to J. L. Davis.

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Davis, J., Wernicke, B., Bisnath, S. et al. Subcontinental-scale crustal velocity changes along the Pacific–North America plate boundary. Nature 441, 1131–1134 (2006).

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