In various tectonic environments, simple shearing or extension of crustal parts has been accommodated by the rotation of parallel faults in an array. Because of its kinematic resemblance to the titling of a row of books on a shelf, the tectonic process may be referred to as a "book shelf" mechanism. Its most important manifestations are cross-faulting between normal faults or parallel wrench faults, the extension of deltaic slope deposits, and all forms of tilted block tectonics.

The process is addressed from a geomechanical point of view to determine geological operating conditions and controlling parameters. Kinematically, one has to distinguish between two basic modes of the book shelf mechanism: the dilational mode, where rotating faults tend to open up and may become migration paths, and the domino style, where the

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rotating faults remain closed. In both cases, formation and rotation of the faults may occur in one tectonic event. Fault displacements may therefore remain small and difficult to detect on seismic records. From the mechanical point of view, one has to differentiate between book shelf operations controlled by an externally imposed simple shearing and those responding to an imposed extension.

The mechanical analysis of book shelf operations induced by simple shearing shows that, under certain conditions, this operation requires less driving shear stress than an accommodation of the imposed shear by shear-parallel faulting. The operation of cross faults between neighboring Riedel faults in a wrench zone is a typical example.

Large-scale rotation of parallel normal faults in domino style (tilted block tectonics) is primarily associated with the extension of ductile substrata. It may be inferred from mechanical arguments and sandbox experiments how the process, and in particular the dip direction of the faults, is controlled by the way the substratal extension progresses, by the direction of a substratal squeeze flow, by the presence of a surface slope, and by the configuration of the rock boundaries that confine the set of faults in the direction of extension.

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