Earthquakes and Lineament Infrastructure

Analyses of the nucleation, propagation and stopping of moderate to large earthquake ruptures, coupled with high-precision studies of background and aftershock micro-earthquake activity, are yielding insights into the infrastructure of major transcurrent fault zones within the seismogenic regime. Curvature and echelon segmentation of a principal slip surface within a ca. 1 km wide main fault zone appear to exert major controls on the starting and stopping of ruptures. Geometrical irregularities of this kind, transverse to the direction of rupture propagation, may be usefully classified into dilational and antidilational jogs, referring to the area change in the plane defined by the slip vector and the pole to planar segments of the fault. Extensional fracture systems linking echelon fault segments across dilational jogs allow long-term transfer of fault slip, but appear to play an especially important role as kinetic barriers impeding or arresting rapid rupture propagation. In fluid-saturated crust the rapid transfer of slip is opposed by suctions arising from rupture-induced differential fluid pressures. Delayed slip transfer, delineated by intense aftershock activity, may then occur as fluid pressures re-equilibrate. Fossil examples of such linking extensional fracture systems are characterized by multi-episode hydraulic implosion breccias. Dilational zones of this kind may migrate along faults or remain fixed for relatively long time periods. They serve as particularly favourable sites for hydrothermal mineralization and may also localize magmatic activity along major lineaments.