HR: 15:10h
AN: G32B-07    [PDF]
TI: Crustal Deformation of the Northern Basin and Range from Measurement with the Global Positioning System
AU: * Hammond, W C
EM: bhammond@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd. MS977, Menlo Park, CA 94025 United States
AU: Thatcher, W
EM: thatcher@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd. MS977, Menlo Park, CA 94025 United States
AB: In northeast California, southern Oregon, and northwest Nevada the three major plate boundary elements of western North America interact, exhibiting a complex pattern of crustal deformation. Between latitudes $40-44\deg$N, deformation associated with translation of the Sierra Nevada microplate, the Cascadia convergent margin, and the extending Basin and Range province overlap. Boundaries for geodetic domains associated with each of these tectonic elements are not well located, and as a result the contributions that each component has on the broad pattern of crustal motion are not well understood. To distinguish among various influences on crustal motion in the northwestern Basin and Range, a 700 km wide network of 86 geodetic sites was established and surveyed in September, 1999, and in June, 2003 with the Global Positioning System (GPS). The network provides a first look at the plate boundary scale deformation pattern of the northwest Basin and Range. We report geodetic velocities and strain rates inferred from the pattern of motion, and use their spatial characteristics to infer the dynamic sources of deformation. Locating the most rapidly deforming areas is necessary to guide the establishment of future sites in the extensional tectonics cluster of the nascent Plate Boundary Observatory. Results indicate that velocities in the eastern half of our network (between $114\deg$W and $119\deg$W longitude) are approximately 2-3 mm/yr westerly with respect to non-deforming North America. Strain rates between $114\deg$W and $119\deg$W are not resolvable, similar to GPS results obtained from campaign and permanent sites east of the Central Nevada Seismic Zone near latitude $39\deg$N. West of $119.5\deg$W the velocity magnitudes begin to increase and change to a more northwesterly azimuth, again similar to the transition between roughly non-deforming central Nevada and the Central Nevada Seismic Zone seen at $39\deg$N. Velocities in the northernmost part of our network, near $43.5\deg$N latitude, have a small eastward velocity component, possibly showing the influence of the Cascadia convergent margin at least as far east as longitude $120\deg$W. Right lateral simple shear deformation is observed near the southwestern part of the network, and is most likely attributable to transform motion between the Sierra Nevada microplate and adjacent northeast California.
DE: 1208 Crustal movements--intraplate (8110)
DE: 1243 Space geodetic surveys
DE: 8109 Continental tectonics--extensional (0905)
DE: 8150 Plate boundary--general (3040)
DE: 8159 Rheology--crust and lithosphere
SC: Geodesy [G]
MN: 2003 Fall Meeting