Remote triggering of high magnitude earthquakes along plate boundaries

It has been shown that large magnitude earthquakes can remotely trigger other large magnitude earthquakes within three days. Such triggering of high magnitude earthquakes is potentially indicative of fault systems at the end of their seismic cycles. Here a method is developed to examine local earthquake history to determine how susceptible a given area is to remote triggering of high magnitude earthquakes. The method is applied to all plate boundaries. Only 14% of global tectonic boundaries are not susceptible to remote triggering, while 86% show susceptibility to varying degrees. The most highly susceptible locations begin triggering at lower magnitudes, dependent on the type of plate boundary. Varying patterns in susceptibility to remote triggering are observed around individual plates. Finite element modeling of the Cocos Plate reveals normal modes which appear consistent with its spatial patterns of high susceptibility. Many of the natural frequencies of the Cocos Plate are closely associated with the frequencies of free oscillations of the earth and could be induced by large earthquakes. Analysis of the stress tensors generated by the normal modes supports a delayed triggering mechanism involving one-sided negative (compressive) stress normal to the plane of the fault.