Abstract Title: Crustal thickness and Moho variability as an indicator
of tectonic activity within the Basin and Range and Colorado Plateau

Abstract Author(s): Hersh Gilbert1, Anne Sheehan2, Matthew Fouch3,
George Zandt1, and Susan Beck1
1University of Arizona, Department of Geosciences, Tucson, Arizona, USA
2University of Colorado, Department of Geological Sciences, Boulder,
Colorado, USA
3Arizona State University, Department of Geological Sciences, Tempe,
Arizona, USA

Abstract: Crustal structure, found by receiver function imaging using
much of the available broadband data from the Basin and Range (BR) and
Colorado Plateau (CP), displays variations in thickness from less than
30 km thick in northern Nevada to close to 40 km in southern Nevada and
central Utah. The changes in crustal thickness within the BR correlate
with temporal patterns of extension, basaltic isotope variations, and
changes in heat flow.  Sparse sampling currently available hinders our
ability to determine if crustal variations coincide with the Wasatch
front, the surface expression of the eastern limit of extension in
central Utah.  The crust appears to gradually thicken to the east
within the CP, suggesting that factors other than crustal extension
contribute to crustal thickness.  Factors associated with extension may
relate to the appearance of the Moho as it has a very different
signature within the BR, where the Moho appears strong, than the CP,
where the Moho appears weak and no extension has occurred.  Elsewhere
in the BR and CP we have deployed a coarsely spaced array of broadband
seismometers in Arizona to study crustal structure from the southern CP
into the BR.  Results from data recorded at these stations corroborate
our previous findings of thinner BR crust. Additionally, we observe low
velocity zones at depths of ~15 and 60 km below the southern CP, which
could help explain the dynamics of plateau uplift.  The combination of
these results indicates the need to improve our understanding of
factors responsible for producing a seismically detectable Moho,
including crustal evolution and differentiation.