| Popis: |
Surface faulting earthquakes are known to cluster in time from historical and palaeoseismic studies in multiple active tectonic settings, including central Greece, southern California and central Italy. However, the mechanism(s) responsible for clustering, such as fault interaction, strain-storage, and evolving dynamic topography, are poorly quantified and hence not well understood. We combine surface dating of active normal fault scarps in central Italy with stress modelling and quartz flow laws, to produce a quantified replication of observed earthquake clustering.We study six active normal faults (including the Mt Vettore fault which ruptured during the 2016 central Italy earthquake sequence) using 36Cl cosmogenic dating. This reveals periods of high and low slip rate, which we interpret to be earthquake clusters/anti-clusters. Interestingly, these changes in slip rate (or clustering) are out-of-phase between neighbouring faults, i.e. when one fault slows down, nearby faults speed up at the same time. To explore the underlying processes driving this out-of-phase clustering behaviour, we link stress transfer caused by slip over clusters/anti-clusters on coupled fault/shear-zone structures with viscous quartz flow laws derived from laboratory experiments.We show that differential stress fluctuates due to fault/shear-zone interactions, and that the magnitude of these fluctuations are sufficient to induce changes in strain-rate and associated slip-rate on neighbouring faults and shear zones. Our results suggest that fault/shear-zone interactions are a plausible and quantifiable explanation for earthquake clustering, thus opening possibilities for process-led and time-dependent seismic hazard assessments. |
