Maximum link distance between strike-slip faults: Observations and constraints

The maximum fault link distance (lateral separation) between two interacting strike-slip faults is studied in relation to fault length (combined length of the two interacting faults). Data collected for laboratory generated strike-slip faults indicate that fault linkage takes place when the lateral separation between two strike-slip faults is less than one tenth of the combined length of the two faults. strike-slip faults developed in clay models require a smaller link distance than those developed in gouge materials. About 98% of the data collected for natural strike-slip faults and 93% of earthquake rupture data derived from KNUEPFER (1989) follow the rule. These observations support a simple scaring relationship for strike-slip faults, i.e., W less than or equal to 0.1 L where W is lateral link distance and L the combined fault length (AN and SAMMIS, 1996a). Two possible explanations are discussed. Assuming a fault continues to be dominantly strike-slip after various fault coalescences, the fault link distance for both compressional coalescence (leading to restraining bend) and extensional coalescence (leading to releasing bend) can be constrained within 0.134 L. Assuming fault coalescence is caused by interaction between breakdown zones at fault tips, then the scaling relationship b = 0.1 l between the size of a breakdown zone, b, and the individual fault length, l (SCHOLZ et al., 1993), leads to the scaling relationship W-max = 0.1 L where W-max is the maximum link distance. The above observed relationship between W-max and L may not hold if faults coalesce through preexisting faults, if a fault has a mixed mode other than strike-slip, or if a fault bend is caused by cross faulting rather than fault coalescence. Limited exposure of natural fault traces may also lead to errors in link distance measurements.