Linkage and evolution of conjugate strike-slip fault zones in limestones of Somerset and Northumbria

Conjugate strike-slip fault zones that cover metre-scale areas at Beadnell, Northumbria, and Kilve, Somerset, were initialed as conjugate vein arrays. Early conjugate faults are linked by the propagation of one fault that eve ntually by-passes the other fault. A model for the development of strike-sl ip faults is presented, using fault and vein geometries and the position of damage zones with respect to the master faults as an indication of the pro pagation direction. This model includes the evolution of networks from (1) the initial random development of vein arrays, to (2) the isolated developm ent of several unconnected conjugate fault segments that pass into vein arr ays, through (3) the intersection of a conjugate set of master faults and l inkage with minor antithetic faults, and the formation of new vein arrays w ith extensional geometries after a linked network of faults is established, to (4) breaching of intersection points by dominant faults, and finally (5 ) the propagation towards oversteps that are breached to form a through-goi ng fault. The geometry of the active structures simplifies with time, as st rain is localised along the master fault, but the complexities are preserve d in the fault walls. (C) 1998 Elsevier Science Ltd. All rights reserved.