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Fault strength in California and western Nevada

Carena, Sara, and Christoph Moder (2008), Fault strength in California and western Nevada, in EGU General Assembly 2008.

The behavior of many major faults on Earth can only be explained if they are assumed
to be much weaker than predicted by Byerlee’s Law. Fault friction can be studied
with numerical forward modeling, but this requires knowledge of the detailed 3-D
geometry of the faults. The latter is now available for most of California, thanks to the
SCEC Community Fault Model (southern California) and to the USGS project “3-D
Geologic Maps and Visualization” (San Francisco Bay and surrounding region).
We modeled a network of approximately 200 faults in California and Nevada with the
finite-element code SHELLS. To avoid having to impose boundary conditions at the
edge of the region, we used a variable-resolution grid, globally coarse but with local
(California and western Nevada) high-resolution representation of actual faults based
on the existing 3-D fault maps. Plates are driven with NUVEL-1 velocities. Fault sliprates
are an output of the model, and we compared them with geologic slip-rates to
determine the best fitting value of effective fault friction coefficient (μ).
Our initial results show that realistic slip-rates on the main plate boundary faults can
only be achieved with very low μgalues. The already low value of 0.17, which was
recommended for California faults by Bird & Kong 1994, seems to be an upper bound.
In fact, the San Andreas fault slip-rate is best fit with μ <0.05. It is also apparent that
a single value of μ does not give the best fit for all faults simultaneously. Minor faults
are best fit with higher μ values (in the 0.1-0.2 range), suggesting that slip-dependent
weakening should be considered when determining the best μ value for specific faults.
In general, the type of faulting obtained from the model fits the data well at low μ,
including the widespread thrusting in the Western Transverse Ranges and the normal
faulting in the Basin and Range. The next step will be to test whether driving plates
using current mantle convection models confirms very low μ.
  author = {Sara Carena and Christoph Moder},
  booktitle = {EGU General Assembly 2008},
  month = {apr},
  title = {{Fault strength in California and western Nevada}},
  year = {2008},
  language = {en},
%A Carena, Sara
%A Moder, Christoph
%D 2008
%T Fault strength in California and western Nevada
%8 apr
%B EGU General Assembly 2008
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