Abstract

Pattern and movement of historical surface faults in western Nevada—typical Basin-Range structures—suggest a control related to strike-slip faulting. Surface faults associated with seven major earthquakes in the past 60 years form a coherent arcuate linear zone (the “Churchill arc”), which appears to have resulted from a specific deformation acting at a single instant in geologic time. The Churchill arc transgresses several mountain ranges, demonstrating that Basin-Range fault-block mountains have not grown independently of one another. A progressive change from dip-slip normal faulting at the north end of the arc to dominantly right-lateral strike-slip faulting at the south end suggests a relationship to the Walker Lane at the south end. The Walker Lane is a major northwest-trending structural zone along which significant right-lateral strike-slip movement has occurred.

A surface fault that formed during one other historical earthquake in this part of western Nevada, in the Excelsior Mountains, is oriented northeasterly and is characterized by left-lateral strike-slip movement.

A possible relationship between block faulting and strike-slip faulting is supported by other evidence besides the historical faults. Experimental evidence of near-surface faulting related to underlying strike-slip faulting, as well as the common association of horst-and-graben structures with large-scale strike-slip faults in several places around the world, implies a genetic relationship between the two different types of structures. Moreover, geologic evidence shows an association between the two contrasting structures in several other parts of the Basin-Range province.

A broad system of conjugate northwesterly and northeasterly strike-slip structures parallel to the San Andreas-Garlock system in California may be present in a large part of the western United States: if so, Basin-Range mountains in general may have formed near zones of horizontal deformation. These transverse lineaments may represent a fundamental structural framework in and near the Basin-Range province.

The general northerly orientation of Basin-Range mountains may be in part related to a structural “grain” established prior to the development of the block-faulted mountains. Pre-Cenozoic structures within and along the western boundary of the Basin-Range province are dominated by nearly north-trending foliations and fold axes that are commonly almost parallel to the present ranges. A few structures older than the Basin ranges are transverse fault zones that trend northwest and northeast; these structures may be ancestral to those of the present regional conjugate strike-slip system here proposed.

Most of the faults in the Churchill arc probably formed above a branch fault of the Walker Lane having right-lateral strike-slip movement. Possibly faults at the north end of the arc resulted merely from north-northeasterly propagation of an inter-montane graben along pre-existing structures.

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