TECTONICS OF THE THINGVELLIR FISSURE SWARM, SW ICELAND

The purpose of this paper is to provide data on the geometry of fractures of the Thingvellir fissure swarm, SW Iceland, and to discuss their formation and development. Most fractures are vertical at the surface and must be the result of an absolute tensile stress. The geometry and arrangement of the fractures indicate that they have grown by coalescence of initially offset small fractures. It is concluded that most fractures attain depths of the order of several hundred meters or less, but that the largest faults attain depths of many kilometers.