Global ubiquity of dynamic earthquake triggering

Earthquakes can be triggered by local changes in the stress field (static triggering(1-7)) due to nearby earthquakes or by stresses caused by the passage of surface ( Rayleigh and Love) waves from a remote, large earthquake (dynamic triggering(8-18)). However, the mechanism, frequency, controlling factors and the global extent of dynamic triggering are yet to be fully understood. Because Rayleigh waves involve compressional and dilatational particle motion (volumetric changes) as well as shearing, whereas Love waves only involve shearing, triggering by either wave type implies fundamentally different physical mechanisms. Here, we analyse broadband seismograms from over 500 globally distributed stations and use an automated approach to systematically identify small triggered earthquakes - the low-amplitude signals of such earthquakes would normally be masked by high-amplitude surface waves. Our analysis reveals that out of 15 earthquakes studied of magnitude (M) greater than 7.0 that occurred after 1990, 12 are associated with significant increases in the detection of smaller earthquakes during the passage of both the Love and Rayleigh waves. We conclude that dynamic triggering is a ubiquitous phenomenon that is independent of the tectonic environment of the main earthquake or the triggered event.