The coast-parallel deep reflection profile ILP-10, located ca. 50 km west of the Norwegian coastline, suggests that major geological Precambrian and Caledonian units well known from the west Norway mainland can be correlated to similar basement units in the shelf area. The offshore continuation of the Nordfjord-Sogn detachment and the Hardangerfjord shear zone related to Devonian extension, bound two N- and NW-facing half-grabens containing lower Palaeozoic rocks of the Caledonian Allochthon. The basement units constitute the substrate for Permer Triassic sediments within the bulk of the study area. Following mid-Permian-early Triassic (ca. 260-240 Ma) stretching, crystalline basement thickness on the Horda Platform was, in places, reduced to some 12-13 km, and the basement rocks are now covered by 8-10 km sediments. The block-bounding and extensional basement-involved master faults of this generation have a spacing of 15-20 km. Permo-Triassic faulting resulted in throws of up to 4-5 km, whereas throws related to the Jurassic-early Cretaceous reactivation are negligible (