Abstract Title: Temporal Distribution of Extensional Strain across the Southern 
Wasatch Fault Zone: Geological Constraints for the GPS Velocity Field.

Abstract Author(s): Harris, R.A., Smith, R.B., Wu-Lung, C., and Meertens, C.  

Abstract: The temporal and spatial distribution of strain along the southern 
Wasatch Fault reveals episodic and transient behavior at a variety of scales. 
GPS velocity fields derived from both continuous and campaign (8 yr. epoch) 
data indicate mostly westward extension across the Wasatch Fault at rates of 
1-3 ± 1 mm/yr. Up to 1-2 ± 1 mm/yr. of westward motion relative to stable North 
America is detected for some stations east of the Wasatch Fault. Preliminary 
nonlinear inversion of the velocity field predicts that the southern Wasatch 
Fault dips west at around 40?, has a dip-slip loading rate of 4.2 mm/yr., and 
is locked at a depth of around 17 km. Measurements of fault planes and 
sense-of-shear indicators reveal that most segments of the southern Wasatch 
Fault are nearly pure dip-slip, low angle faults with a broad zone of 
deformation. The youngest fault scarps offset Lake Bonneville terraces by 15-40 
m, which yield dip-slip rates of 0.9-2.6 mm/yr. over the past 17 ka. However, 
pre-Bonneville alluvial fans show a maximum of 200 m of displacement over time 
scales of 600 ka, which yields slip rates of < 0.3 mm/yr. This difference 
between short and longer-term rates is also manifest in the pattern of faceted 
spurs along the southern Wasatch Fault. Most facets show 250-350 m of nearly 
continuous slip interrupted by intervals of pediment development with little to 
no slip. The youngest facets mostly dip around 40? regardless of rock type, and 
are separated from the next oldest facet by pediments up to 100 m wide. The 
facets may indicate more or less continuous fault activity for periods of 
around 100-200 ka that is interrupted by intervals of quiescence of unknown 
duration. The difference between the loading rates indicated by GPS and slip 
rates inferred from paleoseismic features remains unresolved.