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

Abstract

Continuously recorded Global Positioning
\nSystem (GPS) data from the
\nnorthern Basin and Range suggest that
\ncontemporary deformation is quite slow
\nand broadly distributed, rather than
\nbeing concentrated in the relatively narrow
\nzones of historical earthquakes. Surprisingly,
\nhowever, in north-central
\nNevada, the data indicate rapid, rangenormal
\ncrustal shortening at a rate of
\n2–3 mm/yr in an area where the geology
\nindicates crustal extension via
\nHolocene normal faulting. A possible
\nexplanation for the conflicting geodetic
\nand geologic data is that the region of
\nshortening represents the contractile
\nside of a slowly east-propagating deformation
\npulse generated by the 1915
\nPleasant Valley and 1954 Dixie Valley
\nand Fairview Peak earthquakes. Such
\npulses, which are transient effects not
\nrecorded by faulting, are predicted by a
\nbroad class of physical models, but have
\nonly been observed within a few years
\nafter very large earthquakes, when the
\nsignal is much larger than the long-term
\ndeformation rate. The Basin and Range,
\nand similar areas with a combination of
\nlow long-term deformation rates and
\nlarge earthquakes, may therefore have
\nthe best potential by combining modern
\ngeologic and geodetic data to elucidate
\nfault system behavior, in particular
\nhow transient effects from an earthquake
\non one fault may influence patterns
\nof stress and seismic strain release
\non others. These types of data are essential
\nin developing realistic models of
\nseismic hazard, and in linking
\nshort–time scale observations with
\nlonger term geologic processes.