Hello Helge
The orientation of fracture sets and their relation to each other and to
larger scale structure (folds, adjacent faults or just horizontal or
tilted bedding) are keys to understanding their type and origin. For
example, although shear fractures do not always develop as conjugate
sets, if you do have conjugate facture sets then they must be shear
fractures (Mode II or III). A very nice example of orientation analysis
of fractures in a folded domain (Jura) coupled with detailed
observations of striae and stylolites on the surfaces, is presented in
the textbook of Ramsay and Huber, Volume 2. The measuring of fracture
orientations and their analysis using stereonet or rose diagram is time
consuming but often well worth the effort.
Regards
Mary
Le 21/02/2017 à 21:53, Helge Alsleben a écrit :
> I was wondering what attributes, features or characteristics people commonly use in the field to differentiate between opening Mode I fractures/joints and shear fractures (Mode II or Mode III)?
>
> I understand that Mode I fractures may develop plumose structures, whereas Mode II/III have shear displacement or may even develop slickenlines. However, for the practicality of detailed outcrop studies, where fracture surfaces are often not exposed and displacement on small bed-bound fractures may be very small, those features might not always be observable.
>
> Are there any other features or characteristics that one could look for to differentiate between the different mode fractures in the field with some degree of certainty?
>
> I'd appreciate any comments or suggestions.
>
> Thanks,
> Helge
>
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