Triggered tremor, phase-locking, and the global clustering of great earthquakes

A system of non-linear coupled relaxation oscillators is used to show how the communication between large earthquakes on a global scale can align their seismic cycles to produce a worldwide clustering of large events. Our model builds on recent observations that the seismic waves from a large earthquake can trigger an episode of non-volcanic tremor at the base of a distant fault. We assume that tremor is indicative of creep on the ductile extension of the fault zone that loads its overlying seismogenic layer thus advancing the fault toward failure. If this advance is larger toward the end of the seismic cycle, we show that two or more interacting faults will align their cycles, even if their recurrence intervals are not identical.

► Seismic waves from a large earthquake can trigger an episode of tremor at the base of a distant fault.
► An episode of triggered tremor can advance the seismic cycle on the fault of a fault toward failure.
► If the advance toward failure is larger toward the end of a seismic cycle, then interacting faults can lock into phase.
► Phase-locking provides a physical mechanism to produce clustering of great earthquakes on a global scale.
► Clustering is not caused by direct triggering, but by the gradual alignment of seismic cycles.