Reference lines, fault classification, transform systems, and ocean-floor spreading

Abstract

Transform systems are tectonic situations in which expansion or compression at one end of a strike-slip fault is transformed through the fault into either expansion or compression at the other end. There are six kinds and they have three shapes that are termed S, Z, and U. Transformation is generally abrupt for the sea and generally gradual for the land. For the sea, the sense of strike-slip displacement is inferred from the expansion of the axes of the oceanic rises. There are no reference lines from which the sense of movement can be determined directly, but the system as a whole is generally well established. For the land, reference lines indicate the sense of displacement of the strike-slip faults but the transform systems to which the faults belong is generally less evident than at sea. For the Alpine Fault Zone of New Zealand reference lines indicate a gradual change in nature along its length associated with a gradual change in strike, and indicate that the fault zone connects axes of compression that face in opposite directions. The change in nature is illustrated by a fault stereogram. An attempt is made to determine the transform systems for the other large strike-slip faults, and to relate the systems to the pattern of moving plates indicated by. ocean-floor spreading. The general agreement with the sea-floor spreading hypothesis is good.