Brittle shear zones/fault zones are usually defined by curved brittle P-planes bound by usually straight Y-planes. These shears may affect as a narrow zone within the rock bodies. Brittle sheared lenses of rocks vary in geometry, and the P-planes may curve only near the Y-planes. Fault gouge zones sometimes contain P-planes that help to deduce the shear sense. Fault planes/Y-planes may contain slickensides. See Doblas for detail of slickenside types and their reliable use in shear sense determination. This is despite Tjia questioned reliability of slickensides as shear sense indicators. Deformational structures and especially faulted units within soft-sedimentary structures are quite common.
Keywords: Brittle shear zone; Brittle tectonics; Conjugate faults; Faults; Kinematic indicators; P-plane; Slickensides; Y-plane