Geological and Geophysical Characteristics of the Transform Fault Zones

Abstract

From the point of view of the new concept of global tectonics, oceanic fracture zones consist of one or more transform faults. Their geomorphological descriptions were given for the first time in (Wilson 1965; Menard 1966; Menard and Chase 1970). The authors defined the transform faults as long narrow zones of strongly rugged bottom topography characterized by the existence of linear forms that usually separate topographic provinces with different regional depths. In the transform zones, fault-line ridges are extended parallel to the troughs. It is noteworthy that remains of shallow-water sediments are found on some of the fault-line ridges and bottom terraces. A fracture zone located between contiguous spreading axes is called an active zone. The fracture walls between neighboring spreading axes are characterized by opposite directions of motion. Passive parts of transform faults are located beyond the active zone, but the direction of their motion is the same. Transform faults are distinguished well not only in the ocean bottom topography, but also in anomalous geophysical fields. High fault-line ridges near the walls of faults (mainly between the neighboring parts of spreading axes), deep troughs, faults, and fissures are characteristic of the fracture zones, which represent an assemblage of deep and bottom structures. Anomalies of the magnetic and gravity fields, undulations of the heat flux, and other geophysical data testify to a complex dynamic regime of lithosphere in the fracture zones. Active parts of transform faults are also characterized by the most intense seismicity with clear manifestation of the shear component in earthquake sources.

Author of this chapter is Anatoly Schreider.