GPS VELOCITY CONSTRAINTS ON THE KINEMATICS OF ACTIVE TECTONICS IN GREATER SOUTHERN NEVADA

Although the present-day kinematics of active tectonic deformation for most of the western U.S. is fairly well understood, a solid kinematic framework for the greater southern Nevada region is still absent. The reason for this deficiency is a combination of 1) relatively poor coverage with high-quality geodetic monuments and 2) low deformation rates. Consequently, large uncertainties exist in the rate and style of deformation and hence in the region's seismic hazard.

To develop an accurate model of crustal deformation for southern Nevada, far-field crustal motions need to be well resolved. For instance, any proposed kinematic model will be sensitive to the motions of the Colorado Plateau with respect to the central Great Basin, which behaves as a geodetic micro-block. It is essential to quantify the relative motion between these provinces and to determine whether deformation between them is transferred westward into the eastern California shear zone, or southward into the southern Basin and Range. Thus regional studies must be combined with plate boundary scale kinematic constraints on the motion of large-scale crustal blocks.

We present an up-to-date velocity field for the area derived from continuous GPS measurements. We observe an extension rate of ~1.8 mm/yr across southern Nevada at the latitude of 37 degrees between eastern Nevada and the Colorado plateau. It is still unknown how this motion is distributed across this major structural boundary and whether the relative motion has a boundary-parallel component. We will also discuss the limits placed on relative motion across the Lake Mead and Las Vegas Valley fault zones, and review the latest slip rate estimates of the Death Valley and Stateline faults.

We conclude that there is a need for additional high-quality GPS monuments in the region. The Las Vegas Valley Water District, Plate Boundary Observatory and BARGEN networks include some new sites, but these sites only partly compensate for deficiencies in the network. We have installed a dense network of geodetic markers (20 km spacing) for campaign or semi-continuous observation that will greatly increase our resolving power, but we have currently no financial support to measure those sites, or to expand the network. We will summarize the status of our network, and the potential benefits of additional surveys.