Variation of principial strain axis directions near first-order fault zones on the Island of Rhodes, Greece, and its importance for the interpretation of fault-slip data

Kinematic analysis of small-scale shear faults is ubiquitously applied to infer principal strain directions in brittlely deformed terrains. Often, the directions vary greatly with position. In such cases, non-uniform principal strain directions are frequently interpreted as evidence for successive deformation phases. In the Cape Archangelos area, the pervasive coverage of multi-scale brittle faults lends itself to testing the validity of this practice. Here, kilometer-scale oblique normal faults form first-order faults regarding higher-order, meter- to decameter-scale shear faults. All faults affect Plio-Pleistocene marine strata and thus adhere to neo-tectonic deformation. This allows us to test to what extent principal strain axis orientations, inferred from the inversion of 365 higher-order shear faults, are influenced by their proximity to some 80 first-order normal faults at 14 stations. First-order normal faults form two sets, one striking NNE, the other NNW. As it is unlikely that the overall deformation regime changed during Plio-Pleistocene to Recent times, both sets formed under the same deformation regime. Based on the inversion of higher-order shear faults, principal strain axes indicate either overall N-S or E-W horizontal extension. Fault populations at each station are kinematically homogeneous. This is consistent with faulting during a single deformation regime. Moreover, half of the stations indicating approximately E-W extension are located on or close to first-order normal faults, whereas the other stations showing chiefly N-S extension are located up to hundreds of meters away from these faults. We conclude that the presence of first-order structural discontinuities can significantly influence principal strain axis directions.