The quest for the oldest case of global earthquake triggering

Large earthquakes can trigger other earthquakes at great distances, even on a global scale, through the dynamic stresses imparted by their seismic waves. However, identifying such remote triggering is not always straightforward. It may occur not only instantaneously, during the passage of the seismic waves, but also with a delayed effect—sometimes days or even weeks after the initial event. Recognizing this phenomenon in historical earthquake catalogues, which are incomplete, is particularly challenging, yet it is essential for better understanding its occurrence following rare, large earthquakes and eventually assessing its impact on global, time-dependent seismic hazard.

In this study, we report what may be the oldest documented case of global earthquake triggering, dating back to the eighteenth century. We first integrated and revised global and regional earthquake catalogues from multiple continents, spanning a period of ten years before and after the main earthquake, in order to create a more comprehensive and reliable global dataset. Just after this main event, we observed a statistically significant increase in seismic activity, even at distances greater than 2000 km from the epicentre, followed by an Omori-like decay.

We then modelled the expected global seismic wavefield for the initial earthquake to test whether it could have triggered subsequent remote earthquakes occurred across several continents. For this modelling, we considered the likely magnitude and location of the main earthquake, as well as the focal mechanism of a large, instrumental earthquake most likely caused by the same fault, according to prior research. The subsequent earthquakes occurred precisely in the regions where the calculated dynamic stresses induced by the main earthquake were largest, strongly supporting the hypothesis that they were dynamically triggered.