Dynamics of Plate Boundary Fault Systems from Basin and Range Geodetic Network (BARGEN) and Geologic Data

Abstract

Continuously recorded Global Positioning System (GPS) data from the northern Basin and Range suggest that contemporary deformation is quite slow and broadly distributed, rather than being concentrated in the relatively narrow zones of historical earthquakes. Surprisingly, however, in north-central Nevada, the data indicate rapid, rangenormal crustal shortening at a rate of 2–3 mm/yr in an area where the geology indicates crustal extension via Holocene normal faulting. A possible explanation for the conflicting geodetic and geologic data is that the region of shortening represents the contractile side of a slowly east-propagating deformation pulse generated by the 1915 Pleasant Valley and 1954 Dixie Valley and Fairview Peak earthquakes. Such pulses, which are transient effects not recorded by faulting, are predicted by a broad class of physical models, but have only been observed within a few years after very large earthquakes, when the signal is much larger than the long-term deformation rate. The Basin and Range, and similar areas with a combination of low long-term deformation rates and large earthquakes, may therefore have the best potential by combining modern geologic and geodetic data to elucidate fault system behavior, in particular how transient effects from an earthquake on one fault may influence patterns of stress and seismic strain release on others. These types of data are essential in developing realistic models of seismic hazard, and in linking short–time scale observations with longer term geologic processes.

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