Aydiin,
from a first look some of your outcrops could also be part of faults which failed in hybrid fashion, and in which large segments have no shear indicators at all because they formed as extension fractures. Do you have larger scale observations?
Janos Urai
Prof. Dr. Janos L. Urai
Structural Geology, Tectonics and Geomechanics
RWTH Aachen University, Lochnerstrasse 4-20
www.ged.rwth-aachen.de
On 4 Jan 2015, at 19:45, Robert Twiss <[log in to unmask]> wrote:
Aydiin,
First, I would say that if you are looking at fault motion indicators, you are actually doing an instantaneous strain inversion (equivalent to a strain rate inversion), not a stress inversion (see "Twiss, R.J. and J.R. Unruh. 1998. Analysis of Fault-Slip Inversions: Do They Constrain Stress or Strain Rate? Jour. Geophys. Res., 103(B6): 12205-12222". See also "Twiss, R. J. and J.R. Unruh. 2007. Structure, deformation, and strength of the Loma Prieta fault, northern California, USA, as inferred from the 1989–1990 Loma Prieta aftershock sequence. Geological Society of America Bulletin, 119(9): 1079-1106" for an example of how the instantaneous strain interpretation of fault slip inversions makes much more sense, and provides greater insight into the fault mechanics, than the stress interpretation).
Second, see "Twiss and Moores, 2007, Structural Geology, 2nd Ed., W.H. Freeman & Co." Figs. 3.16, 3.17, and 3.18 for illustrations of brittle shear sense indicators, and see the associated text for discussion.
Finally, it is difficult to interpret the shear sense just from your photos, but this is what it seems to me I can see:
• Your photo 6.JPG looks to me like the shadowed faces trending roughly top to bottom in the photo are plucked congruous faces of extension fractures with striated incongruous steps connecting them. Fig. 3.17A in Twiss & Moores shows the relation of shear sense to the extension fractures, and Fig. 3.17E shows the congruous plucked faces (light color) with the incongruous steps (striated). If this is correct, I would infer the missing block moved to the right in the photo.
• Your photo 8.JPG appears to have some slickenfibers right in the middle of the photo inclined at a very small angle to the shear plane and parallel to the lineation. If true, these would be similar to the slickenfibers forming congruous steps as in Fig. 3.16 in Twiss & Moores. This would suggest the missing block moved up and to the right in your photo. At the very top of the photo a little to the right of the middle, there appears to be a plucked extension fracture trending at almost 90° to the lineation and forming a congruous step connecting two striated fractures. This would be like the extension fractures in Figure 3.17A forming plucked congruous steps connecting striated fractures as in Fig. 3.17E in Twiss & Moores. This would give a sense of shear consistent with that inferred from the slickenfibers.
• In your photo 3.JPG, it seems like on the right side near the middle, there may be some lunate fractures, but I cannot see whether or not they are striated, as indicated in Fig. 3.17D in Twiss & Moores, so I cannot infer a shear sense.
• In the other photos, I cannot see clearly enough to interpret any shear sense.
As always, once you have come to a conclusion about the shear sense, you should then look again to see if you can convince yourself that there is evidence for the opposite shear sense. If you can convince yourself either way, the evidence is probably inconclusive. Shear sense indicators are often difficult to read clearly, and one has to be very careful not to notice only the evidence that supports a preconceived idea.
Hope this is of some help.
Cheers,
Rob Twiss
On Jan 4, 2015, at 3:13 AM, aydin CICEK wrote:
> Dear Sir/Madam,
>
>
>
>
>
>
>
>
> 6.JPG
> aydin CICEK shared from Dropbox
> View on www.dropbox.com
> Preview by Yahoo
>
>
>
>
>
>
>
>
>
> 4.JPG
> aydin CICEK shared from Dropbox
> View on www.dropbox.com
> Preview by Yahoo
>
>
>
>
>
>
>
>
>
> 3.JPG
> aydin CICEK shared from Dropbox
> View on www.dropbox.com
> Preview by Yahoo
>
>
>
>
>
>
>
>
>
> 2.JPG
> aydin CICEK shared from Dropbox
> View on www.dropbox.com
> Preview by Yahoo
>
>
>
>
>
>
>
>
>
> 8.JPG
> aydin CICEK shared from Dropbox
> View on www.dropbox.com
> Preview by Yahoo
>
>
>
>
>
>
>
> I am working on paleostress analysis. I am not sure on sense of motions of some faults included in attachments. I am a bit confused of some of them. Could anyone help me to assign the sense of shear and type of the criteria used in.
>
>
> Kind regards,
>
>
> IN MY VIEW
>
> SENSE OF PREDICTED SHEAR TYPE OF PREDICTED CRITERIA
> 1- sinistral 1- RIEDEL FRACTURES, CHATTER MARKS
> 2- dextral 2- RIEDEL FRACTURES
> 3- sinistral 3- RIEDEL FRACTURES
> 4- dextral 4- "PO" AND "PT" type structures (PETIT 1987)
> 5- dextral 5- "PO" type structures (PETIT 1987)
> 6- dextral 6- "PO" type structures (PETIT 1987)
> 7- dextral 7- "Slickolites" and some "RO" type fractures (PETIT 1987)
> 8- dextral (?????) 8- some graing plucking marks (PETIT 1987)
> 9- sinistral 9- fault step just above the marker (???)
> 10- sinistral 10- some PT type structures, grain plucking marks...etc (PETIT 1987)
>
> Aydın CICEK,
|