On the Constancy (or Not) of Fault Slip Rates and Strain Accumulation Rates on Major Strike-Slip Faults

Abstract:

The degree to which fault slip rates and elastic strain accumulation rates are constant in time and space is one the most fundamental, unresolved issues in modern tectonics. Increasingly detailed geologic and geodetic observations from many continental strike-slip faults reveal several well-constrained examples in which strain accumulation and release rates are not temporally constant, being characterized instead by strain super-cycles that span multiple-earthquake cycles and geodetically constrained slip-deficit rates that are either much faster or much slower than the long-term average slip rate of the fault. Such observations call into question a number of basic assumptions about the behavior of faults, including most especially the notion that fault slip and elastic strain accumulation rates are relatively constant through time, as well as the idea that individual faults can be examined in isolation, rather than as components of mechanically integrated systems. In this talk, I will discuss evidence from a number of well-constrained examples in which both strain release (i.e., fault slip) and strain accumulation (fault “loading” rates) are decidedly non-constant. Various mechanisms have been suggested to explain these behaviors, although these remain poorly understood, and deciphering the controls of earthquake occurrence in time and space remains an exciting research frontier.