  Segment lengths along major strike-slip faults exhibit a size dependency
related to the brittle crust thickness. These segments result in the formation
of the localized 'P-shear' deformation crossing and connecting the initial
Riedels structures (i.e. en-echelon fault structures) which formed during the
genesis stage of the fault zone. Mechanical models show that at all scales, the
geometrical characteristics of the Riedels exhibit dependency on the thickness
of the brittle layer. Combining the results of our mechanical discrete element
model with several analogue experiments using sand, clay and gypsum, we have
formulated a relationship between the orientation and spacing of Riedels and
the thickness of the brittle layer. From this relationship, we derive that for
a pure strike-slip mode, the maximum spacing between the Riedels are close to
three times the thickness. For a transtensional mode, as the extensive
component becomes predominant, the spacing distance at the surface become much
smaller than the thickness. Applying this relationship to several
well-characterized strike-slip faults on Earth, we show that the predicted
brittle thickness is consistent with the seismogenic depth. Supposing the
ubiquity of this phenomenon, we extent this relationship to characterize
en-echelon structures observed on Mars, in the Memnonia region located West of
Tharsis. Assuming that the outer ice shells of Ganymede, Enceladus and Europa,
exhibit a brittle behavior, we suggest values of the corresponding apparent
brittle thicknesses.
