Fault structure, wear mechanisms and rupture processes in pseudotachylyte generation

Abstract

Fault-generated pseudotachylyte is found within both cataclastic and mylonitic host rocks suggesting that rapid catastrophic displacements have occurred at a variety of depths within paleoseismogenic zones. Pseudotachylyte-bearing fault zones represent a composite of structural features associated with the process of earthquake rupture propagation and coseismic slip. The development of multiple pseudotachylyte veins in fault linkages, duplexes, sidewall ripouts, en echelon arrays and brittle zones suggests repeated rupturing during a series of characteristic earthquakes. Each earthquake, as a coseismic slip event, can be subdivided into initial rupture, acceleration, stable sliding and final deceleration stages. These evolve through distinctive sequences of wear and deformation mechanisms that vary with sliding velocity, duration of slip, total displacement and the hydrodynamics of the developing fault zone. Slip is thought to proceed toward surface refinement and possible frictional melting following the propagation of leading shear fracture process zones. The passage of the initial process zone of oblique fracturing would be followed by linkage to a throughgoing structure with asperity reduction through brecciation, comminution and refined cataclastic flow for frictional melting in an abrasive wear-dominant model. At greater depths in the presence of mylonitic anisotropy, slip would proceed through initial layer-parallel surfaces and duplex linkages with rapid surface refinement through plastic smearing and laminar flow for frictional melting in an adhesive wear-dominant model.