Abstract Title: Using tectonic geomorphology to study pulses of active
deformation, Western Great Basin Province, USA

Abstract Author(s): Anke Friedrich1,2, Yves Gaudemer2, Geoffrey King2,
Rolando Armijo2 , and Manfred Strecker1- 1. Institut fur
Geowissenschaften, Universitat Potsdam. 2. Laboratoire Tectonique, IPG de
Paris.

Abstract: One of the goals of the Plate Boundary Observatory is to
determine how continental lithosphere responds to changes in geodynamic
driving forces. Because many geodynamic processes occur on timescales
much longer than geodetic recording time intervals (years to tens of
years), longer term deformation measurements are required. On what
timescale, however, should these longer term (geological) measurements
be made to allow a meaningful extension of geodetic time series?
Traditional geological and tectonic studies appear to indicate that
continental fault systems are active continuously for millions of
years, whereas more precise paleoseismological measurements often show
highly irregular fault slip behavior. In order to study the evolution
of individual fault systems, measurements are needed on an intermediate
timescale: long enough to average over many seismic cycles, but short
enough to provide the incremental strain history. For continental fault
systems such as those of the Basin and Range Province (c. 10 nstrain at
present, e.g., Bennett et al. 2003, Friedrich et al. 2003), the
expected sensitive timeinterval is a few hundred thousand years and the
expected signal size should range from several meters to a few hundred
meters. In climatically sensitive regions, such as the semi-arid Great
Basin, such surface deformation features may, on one hand, be preserved
extremelly well over several hundred thousand years; On the other hand,
however, such regions are also sensitive to weather extremes and
medium-term climatic variations (tens of ka) as exhibited during the
Pleistocene cold (wet) period, which may result in climatically
dominated landscapes. In the Great Basin, both examples represented.
For example, (1) on the 10 ka timescale, many internally drained basins
filled to large lakes (Bonneville and Lahontan) which left thick
sedimentary sections covering most pre-existing tectonomorphic
features; and (2) on the 500 ka timescale, near vertical surface
deformation resulted in growth of new fault structures that have
affected drainage, erosion and deposition patterns. We document such
tectonogemorphic signals for the eastern limit of the Carson Sink
extensional region in the western Great Basin, along the W-flank of the
Shoshone Range and Cortez Mountains, and speculate on their tectonic
significance.