Transcurrent faults in continental areas

Abstract

Seismic fault-plane solutions, displacements observed during historic earthquakes, and an increasing number of geological reports of active transcurrent faults in many parts of the world all suggest that transcurrent faulting is a far more important tectonic process than has usually been recognized. Characteristic features of active transcurrent faults-easily overlooked in the absence of aerial photographs-include: abundant Recent scarps that often show a scissoring relationship to one another; elongate closed depressions; consistently offset streams; and unique rift topography that is remarkably linear over distances of hundreds of kilometers. Thrusts that steepen abruptly with depth typify many transcurrent faults at the base of steep mountain fronts and have led to delays in recognition in some areas. Most puzzling of the great transcurrent fault zones are those of the circum-Pacific rim, where the relationship between major transcurrent faults of the continental margins and structures of the deep ocean floor is obscure. The Gulf of California is one region that appears transitional in that it combines many attributes of extensional rift valleys with those of transcurrent faults. Transcurrent displacements, particularly those of large magnitude, add to the attractiveness of the continental drift hypothesis, but demonstrated movements in the circum-Pacific zone are largely parallel to continental margins and thus fail to fit neatly with most theories of orogenesis and drift.