Comparison of Moment Rates from GPS Observations and Late Quaternary Paleoearthquakes on the Wasatch Fault, Utah Abstract


  • The Wasatch fault marks the boundary of stable North America and the extensional Basin and Range province, and is capable of producing large, M6-7 earthquakes. Velocities from the University of Utah Wasatch Front permanent GPS network are analyzed to determine horizontal strain rates and extension rates across the Wasatch fault zone, Utah. Extension rates across the fault decrease from 2.24 ± 0.04 mm/yr in the north to 1.89 ± 0.04 mm/yr to the south. Observed GPS velocities are interpolated into strain rates and mapped, revealing that the highest strain rates are at the southern fault at 0.05x$10^{-6}$ 1/yr across a ~100 km profile; strain rates to the north are 0.02x$10^{-6}$ 1/yr but spread over a wider, ~150 km profile, indicating that another fault, possibly the East Great Salt Lake fault and/or Oquirrh fault, may be contributing to deformation. We construct dislocation models to determine whether additional faults can be identified, and whether the Wasatch fault geometry (strike, dip, slip rate) varies between segments. Strain rates are converted to geodetic moment loading rates for north, central, and south segments of the fault and compared to the Late Quaternary moment loading rates from prehistoric earthquake magnitudes based on fault trenching studies and averaged over time. Geodetic moment rates increased from north to south, from ~7x$10^{23}$ to 1x$10^{24}$ dyne cm/yr, exceeding the geologic moment rates by factors of ~2-4. The geodetic rates represent contemporary deformation and offer an alternate method to assess elastic strain accumulation on the Wasatch fault under present-day tectonic stresses.


publication date

  • 2011

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