Architecture of onshore fault zones

Abstract

We review research on the architecture of onshore fault zones. Drilling the Nojima Fault was a turning point in studies of shallow brittle faults, stimulating research on their hydrological and frictional properties. Investigations of the deep seismogenic zone of faults such as the Median Tectonic Line (MTL) have identified deformation mechanisms such as pressure solution, creep, and crystal plasticity of mica in foliated cataclasite. Cataclastic damage causes increased intracrystalline strain in surrounding rocks. Several studies of the Asuke shear zone and the MTL have estimated the stress and strain rate in the brittle–plastic transition zone. Some studies of the Hatagawa fault zone have revealed the processes involved in fracture nucleation and documented heterogeneous deformation on the scale of tens of kilometers. In the lower crust of the Hidaka metamorphic belt, evidence was found for plastic deformation of plagioclase and pyroxene by dislocation creep. It was also found that formation of fine-grained aggregates during deformation results in weakening by a change in deformation mechanism from dislocation creep to grain boundary sliding. Recently, evidence of fracturing has been found in deformed lower crustal rocks, possibly resulting from stress concentration at the down-dip termination of earthquake ruptures, although further studies are needed to confirm this inference.