I actually agree with Terry,
All attempts to make an exhaustive paleostress analysis from fault-slip data are still questionable, despite the huge amount of papers made on the subject. This for several reasons, among which the followings.
A "classical" technique to separate different fault populations in terms of stress fields and sequence in time, and used in many softwares, is the cross-cutting relationships, late faults being "normally" considered as cross-cutting older ones. However, this cannot for sure be a general statement . Indeed, well oriented faults with respect to the overall stress (deformation) field will be more efficient (i.e. higher displacement rates) than those less well oriented. In a progressive deformation view, older faults are often the best oriented and the most efficient. Thus, old fauls with high displacement rates may off-set younger ones with lower displacement rates. This was shown by analogue experiments.
Gapais
D., Fiquet G. & Cobbold P.R. 1991. Slip system domains -3- New insights in
fault kinematics from plane-strain sandbox experiments. Tectonophysics, 188:
143-157.
Another reason is that, except where the bulk strain is neglible (no strain?), faults do rotate during progressive deformation. As a consequence, even in relatively moderately deformed zones, fault patterns and attached attitude of principal axes of fabric ellipsoid do reflect strains and not stresses. This was actually shown in the following paper:Gapais D., Cobbold P.R., Bourgeois O., Rouby D. & Urreiztieta de M. 2000. Tectonic significance of fault-slip data. J. Struct. Geol., 22: 881-888.
More generally, and I think was never published, the only deformation mechanism that produces faults that may not rotate during deformation, is heterogeneously distributed pressure solution, as classically observed in low grade limestones where deformation is accommodated along discrete stylolites (dissolution), and tension gashes (precipitation). There, it is possible to accumulate strains without fault rotations. Amazingly, the first important developments of determination of stress tensors from fault patterns were made in limestones (e.g. in southeastern France)... Just think about it.
I hope these simple comments may help you in your research.
Cheers
Denis
Le 12 mars 2013 à 16:28, Pavlis, Terry L a écrit :
No program will save you from heterogeneous data. This is common in paleostress studies, and generally results from changing stresses or time, or finite strain destroying the assumptions in paleostress analysis.
One approach would be to use the "odd axis" method of Krantz. It tends to be more robust when you have messy data, but it won't save you if it really is a mess.
Terry Pavlis
From: Tectonics & structural geology discussion list [mailto:[log in to unmask]] On Behalf Of Rajesh Pandey
Sent: Tuesday, March 12, 2013 5:58 AM
To: [log in to unmask]
Subject: Palaeostress analysis
Respected Geoscientists
I am working in Palaeo-stress Pattern analysis in Himalaya using fault slip data. But I am facing problem regarding the heterogeneity of data sets. Kindly let me know any software using which I can convert heterogeneous data set to homogeneous.
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Regards-
Department of Earth Sciences
Indian Institute of Technology Roorkee
Denis Gapais
Géosciences Rennes
UMR 6118 CNRS
Université de Rennes 1
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France
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