Analysis of the static stress field around faults lying along and intersecting a bimaterial interface

SUMMARY Major faults are known to lie along material interfaces, including plate interfaces and tectonic lines. Recent high‐precision observations have revealed that there are also faults in the vicinity of material interfaces. This suggests that slip on a fault and stress changes near one can be affected significantly by the presence of a material interface. In this paper, we develop a new mathematical framework to derive an expression for a static slip response function by drawing on properties of complex functions. Our method is characterized by its unique ability to analyse both a fault lying along a material interface and a fault intersecting a material interface under a unified framework. A few previous studies have theoretically dealt with the problem of slip on a fault that intersects a material interface, but their mathematical techniques were so complicated that they had only limited utility for seismological applications. By contrast, our mathematical framework has a simple structure thanks to the characteristics of the complex functions. Using our formula, one can easily calculate the fault slip and the static stress changes nearby, if only the stress drop on the fault is given. The static stress is represented as a sum of stress changes due to the slip and a background stress that is generally discontinuous across a material interface. Understanding of the static stress state around a fault has important implications for evaluating the likelihood of secondary failures. We find that, when the fault is located along, or in the vicinity of, a material interface, the background stress plays a key role in the formation of the stress state around a fault, and accordingly also in the triggering of secondary failures.