The crustal-scale Outer Hebrides Fault Zone (OHFZ) in NW Scotland is a complex fault zone which cuts Precambrian gneisses and which was active, with varied kinematics, at several epochs between the Proterozoic and the Mesozoic. It is outlined by a series of fault rocks formed under ductile to brittle conditions. The southern part of the Outer Hebrides Fault Zone, exposed in South Uist, Eriskay and Barra, is outlined by pseudotachylytes and cataclasites presumably formed by reverse motion during the brittle stages of the Caledonian orogeny about 430 Ma ago. Analysis of published geological maps and detailed field mapping between latitudes N56°54' and N57°17' show that the OHFZ consists of two segments. Between N57°07' and N57°17', the northern segment emplaces a banded granulite-textured metadiorite, forming the so-called Corodale gneiss, upon Lewisian gneiss. This fault segment is characterised by moderate deformation in the footwall. The hanging-wall consists of a pseudotachylyte sole whose thickness is comprised between 2 and 10 m and which is overlain by a cataclastic zone whose thickness ranges from a few meters to more than 50 m, locally reaching 250 m. Between N56°54' and N57°07', the hanging-wall and footwall of the southern segment both consist of Lewisian gneiss but with different metamorphic grades. Unlike the northern segment, the southern segment is characterized by numerous pseudotachylyte-bearing thrust surfaces along which the pseudotachylyte thickness seldom exceeds 0.5 m. In summary, seismic deformation along the northern segment appears localized and is associated with significant cataclasis, whereas along the southern segment, seismic deformation is essentially distributed, with limited formation of pseudotachylyte and very little cataclasis. The segmentation likely reflects the contrasted mineralogical compositions and the texture of the rocks from the hanging-wall. The Corodale gneiss mainly consists of an assemblage of minerals (opx-cpx-gt-pl) whose friction melting susceptibilities are higher than the mineralogical assemblage of the Lewisian gneiss (qz-pl-kf- bi and minor hbl-px). Similarly, unlike the Lewisian gneiss, the Corodale gneiss is devoid of any planar fabric. These differences may account for the preferred development of cataclasites in Corodale gneiss. The segmentation is further discussed by comparison with modern earthquake ruptures.