Julia,
Your objective is a difficult one. There remains much uncertainty
about
how to decompose fault slip data into events. Johnson (1995) provides a nice
review about the activity of faults associated with a non-plane strain brittle
deformation. He also discusses how fault orientation varies as a function of
the state of stress. The issues he raises are important ones to consider given
that they challenge some critical assumptions in the paleostress method.
You might try a different approach. Rather than trying to
immediate decompose
your data into fault event, you could ask the question what is the integrated
brittle strain that has resulted from all of the faults. You may find that
this result
provides a more robust way to start interpreting your data. In this regard, the
Twiss et al micropolar method may be a useful approach in that it focuses
on the
the deformation produced by the fault slip as indicated by the pattern of
slickensides.
I have included references below. Note that historically, this
issue of how to
invert fault data for stress or strain has tended to generate many strong
and divergent
opinions. This forum may be a good one to hear what the current thinking is.
Cheers,
Mark
Johnson, A. M., 1995, Orientations of faults determined by premonitory
shear zones: Tectonophysics, v. 247, p. 161-238.
Twiss, RJ and MJ Gefell (1990) Curved Slickenfibers - a new Brittle Shear
Sense Indicator With Application to a Sheared Serpentinite. IN: JOURNAL OF
STRUCTURAL GEOLOGY. 471-481. PERGAMON-ELSEVIER SCIENCE LTD. OXFORD.
Twiss, RJ, GM Protzman and SD Hurst (1991) Theory of Slickenline Patterns
Based on the Velocity-gradient Tensor and Microrotation. IN:
TECTONOPHYSICS. 215-239. ELSEVIER SCIENCE BV. AMSTERDAM.
Twiss, RJ, BJ Souter and JR Unruh (1993) The Effect of Block Rotations on
the Global Seismic Moment Tensor and the Patterns of Seismic P-axes and
T-axes. IN: JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH. 645-674. AMER
GEOPHYSICAL UNION. WASHINGTON.
Unruh, JR, RJ Twiss and E Hauksson (1996) Seismogenic deformation field
in the Mojave block and implications for tectonics of the eastern
California shear zone. IN: JOURNAL OF Twiss, RJ and JR Unruh (1998)
Analysis of fault slip inversions: Do they constrain stress or strain
rate?. IN: JOURNAL OF GEOPHYSICAL RESEARCH-SOLID EARTH. 12205-12222. AMER
GEOPHYSICAL UNION. WASHINGTON.
At 09:22 AM 2/7/2005, you wrote:
>Dear list members,
>
>I currently try to separate stress tensors from heterogeneous fault-slip data
>collected at the eastern margin of the Tibetian Plateau, where I found six (or
>more?) superposed deformation phases (D1 to D6/7/8?) - the first two of which
>record ductile, the succeeding phases brittle deformation.
>
>The data set for the brittle faults (D3 to D6/7/8?) comprises the
>orientation of
>the faults and associated slickensides or slickofibres on the fault
>surface and
>the sense of movement derived thereof. Fault planes frequently exhibit two,
>seldomly three different sets of lineations. However, overprinting
>relationships are usually unclear, as lineations have formed on several
>parallel planes within the 1-3 cm width of the fault ("zone") and the
>individual layers have weathered off irregularly. Fault planes have therefore
>not only been newly built, but have certainly been reactivated and
>demonstrably
>been rotated.
>
>There is some control of the approximate orientation of the paleo-
>stress-field,
>derived from the orientation of fold axes and large-scale shear zones.
>For a more precise calculation of the stress tensors from the fault-slip data,
>however, I am in need of some computer software capable of differentiating
>between tensors of several deformation phases.
>
>Does anyone of you know some software that could perform such operation? I am
>aware of the recent publications of
>
>Liesa and Lisle: Realibility of methods to separate stress tensors from
>heterogeneous fault-slip data. J Struc Geol, 26 (2004), 559-572
>
>and Yamaji: The multiple inverse method: a new technique to separate stresses
>from heterogeneous fault-slip data. J Struc Geol 22 (2000) 441-452 (not so
>sucessful with my data)
>
>Any hint is highly appreciated,
>
>Regards
>Julia
>
>
>Dr. Julia Kramer
>Postdoctoral Researcher
>Economic Geology Research Institute(EGRI)
>School of Geosciences
>University of the Witwatersrand
>Private Bag 3
>2050 Wits, Johannesburg
>South Africa
>
>Office: +27-11-717 66 11
>Mobile phone: +27-72-997 50 72
>Email: [log in to unmask]
>Or: [log in to unmask]
>
>----------------------------------------------------------------
>This message was sent using IMP, the Internet Messaging Program.
________________________________________________________________________
Mark Brandon, Professor, Dept. of Geology and Geophysics
Yale University, P.O. Box 208109, 210 Whitney Avenue, New Haven, CT 06520-8109
e-mail: [log in to unmask]
wk. phone: +203-432-3135, wk. fax: +203-432-3134
Dept. Web site: http://www.geology.yale.edu
Brandon's site: http://www.geology.yale.edu/~brandon
________________________________________________________________________
|