Subsurface Fault Geometries and Crustal Extension in the Eastern Basin and Range Province, Western U.S

Maria Soledad Velasco
University of Arizona, Dept. of Geosciences Tucson, AZ; [email protected]

The correlation between subsurface fault geometries and structures observed at the surface is important for understanding fault system mechanics. A number of seismic reflection lines, present-day crustal deformation data from continuous GPS, and surface geology were used to investigate the relationships between interseismic strain accumulation, subsurface fault geometry, and geologic slip rates on seismogenic faults across the eastern Basin and Range. The seismic reflection data show recent activity along high-angle normal faults that become listric with depth and appear to sole into preexisting décollements, reactivating them. These observations are consistent with the mapped geology in areas that have experienced significant extension. Crustal deformation data was inverted for a model consisting of a buried dislocation source in a homogeneous elastic half space. The estimated model results show a low-angle dislocation (~8-20°) at a locking depth of ~7-10 km and slipping at 3.2±0.2 mm/yr. The predicted dislocation is in general agreement with seismic reflection data, and suggests an active regionally extensive sub-horizontal detachment in the eastern Basin and Range. This result has implications for crustal rheology, and suggests that geodesy might, under some circumstances, serve as an appropriate tool for imaging deeper crustal structure. The shallower listric normal faults observed on the seismic data were interpreted as reactivated Sevier-age structures that are connected at depth with the regionally extensive detachment. This low-dipping surface is also interpreted as a reactivated thrust that is located along the brittle-ductile transition under the present-day extensional eastern Basin and Range.

AAPG Search and Discovery Article #90083 © 2008 AAPG Foundation Grants in Aid