ANALYSIS OF THE RELATIONSHIP BETWEEN DISPLACEMENTS AND DIMENSIONS OF FAULTS

Data on the maximum lateral dimensions (widths) and maximum displacements on normal faults and thrusts, with maximum displacements from 4 mm to 40 km, are used to derive an expression relating width, displacement and material properties. The basis of this expression is a fault growth model in which width is proportional to the square root of displacement. Width/displacement ratios vary systematically with size of a fault from values of ca 30,000, which are characteristic of a single slip event, to about 10 in the case of thrusts with displacements of 40 km. Data on widths and maximum displacement of 308 fault traces recorded on British coalmine plans are shown to be consistent with variation of shear modulus of about half an order of magnitude. Data on 58 further fault traces are shown to be consistent with the fault growth mode. The increase in dimensions of a fault is a postseismic process of subcritical crack propagation for which the significant material property is fracture toughness.