Tidal resonance mechanism identified as trigger for slow earthquakes

A new geophysical study published in the Journal of Geophysical Research (JGR Solid Earth) has identified a mechanism explaining how the gravitational pull of the Sun and Moon can trigger slow earthquakes.

Researchers from institutions including the École Normale Supérieure, the Bureau de Recherches Géologiques et Minières, and the University of Tokyo utilized mathematical modeling to demonstrate that tectonic resonance is the key driver. While the tidal stresses exerted on the Earth's crust are extremely small—often only a few kilopascals—they can amplify the movement of deep faults through a resonance effect, similar to how a rhythmic push can increase the swing of a pendulum.

This phenomenon is particularly observable in subduction zones along the Pacific Ring of Fire, including regions near Japan, Taiwan, and North America. Unlike destructive, sudden earthquakes, these tidal-induced movements result in ‘slow earthquakes’ or deep tremors that release accumulated tectonic energy gradually over hours, days, or weeks rather than in a single violent burst.