Characteristic aspects of earthquake recurrence

The term “characteristic” is frequently used in discussions about earthquake recurrence, sometimes referring to the timing of earthquakes and sometimes referring to slip at a point or slip along a certain portion of a fault. For example, numerous tectono-geomorphic studies have reported that slip accumulation occurs via repetition of same-size, characteristic slip increments. Following the concept of stress renewal, this observation of same-size slip increments led to the hypothesis that the timing of large, surface-rupturing earthquakes may also be characteristic i.e., periodic. Paleoseismic investigations however commonly indicate that the recurrence time of surface rupturing earthquakes is not exhibiting this simple, predictable behavior. In fact, geomorphic and stratigraphic records seem to contradict each other in that regard. In my presentation, I discuss examples of observed earthquake recurrence, constrained by geomorphic and stratigraphic evidence and put them in relation to results from physics-based multi-cycle rupture simulation and statistical considerations. I explore whether the reported same-size slip increments might be result of quasi-periodic climatic forcing as opposed to tectonic forcing. In doing so, I show that the discrepancies between stratigraphic and geomorphic records are related to respective differences in resolution and preservation potential. The accumulation of slip along individual fault sections is not exclusively linked to but dominated by the occurrence of same-size slip increments i.e., characteristic earthquakes. Periodic climatic forcing cannot plausibly explain this behavior. Further, the depth-dependence of fault strength, expressed in the (a-b) friction parameter, provides a physical explanation for this dominantly characteristic behavior in slip accumulation.