Abstract

A second generation of BIRPS profiles combine with older data to form a loose (10 by 40 km spacing) grid over the offshore projection of the Moine Thrust. These profiles show clear reflections that arguably represent fault plane reflections from the Moine and related Caledonian thrust structures in the location suggested by some earlier workers. Reflectors predominate at two structural levels: 8-10 km (2.5-3.5 sTWT) and 13-16 km (4.0-5.5 sTWT) depths. The deeper set appears to define an antiformal stack of thrusts or duplex with possible continuation to deeper levels. By analogy with onshore sections and after subsequent extension is restored, this deeper set correlates with the Moine Thrust onshore. The shallower set aligns with normal faults that bound half grabens filled with Devonian and Permo-Triassic rocks. This set correlates with the Naver Thrust after similar restoration. Normal faulting appears to have reactivated some of the thrusts, increasing their reflectivity. Detailed stacking- and interval-velocity studies indicate that an increase of about 1-2km s−1occurs across the reflections here associated with the two fault zones. The overall reflection pattern is consistent with a complex stack of thrust sheets, but lack of resolution prevents a complete structural analysis.

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