FAULT ZONES FROM TOP TO BOTTOM: A GEOPHYSICAL PERSPECTIVE

Geophysical studies of the Earth's crust, including fault zones, have greatly developed over the past 80 years. Among the first methods to be employed, seismic refraction and reflection profiles were recorded in the North American Gulf Coast to detect salt domes which were known to trap hydrocarbons. Seismic methods continue to be the most important geophysical technique in use today due to the methods' relatively high accuracy, high resolution, and great depth of penetration. However, in the past decade, a much expanded repertoire of seismic and non-seismic techniques have been brought to bear on studies of the Earth's crust and uppermost mantle. Important insights have also been obtained using seismic tomography, measurements of seismic anisotropy, fault zone guided waves, borehole surveys, and geo-electrical, magnetic, and gravity methods. In this paper we briefly review recent geophysical progress in the study of the structure and internal properties of faults zones, from their surface exposures to their lower limit. We focus on the structure of faults within continental crystalline and competent sedimentary rock rather than within the overlying, poorly consolidated sedimentary rocks. We find that 1) The width of the fault damage zone is proportional to total fault offset, 2) Large strike-slip faults have vertical low-velocity, high-conductivity zones, 3) Anomalous fault zone properties undergo temporal “healing” after a large earthquake, and 4) Fault zones can either act as a fluid conduit or an impermeable barrier, depending on composition and history.