Researchers at PSL University used computer simulations to show how tidal forces from the sun and moon can cause gradual fault slips known as slow earthquakes.

A team of geoscientists led by Yishuo Zhou at PSL University in Paris has developed computer models to investigate how the gravitational pull of the sun and moon triggers slow earthquakes. These events involve gradual energy release along fault lines, differing from the sudden movement of ordinary quakes. The findings, published in the Journal of Geophysical Research: Solid Earth, suggest that resonance plays a critical role in how these celestial forces influence fault behavior.

Simulating Fault Dynamics

To understand the mechanism, researchers created a digital spring-block model that simulates a block sliding along a fault. They incorporated established friction rules to account for changes in rock strength during movement or periods of rest. The team then applied repeating, wave-like forces to the model to represent the tiny stresses caused by solar and lunar gravity.

The Role of Resonance

The simulations demonstrated that slow earthquakes are triggered when the timing and force of tidal pulls align with the fault's natural response rate, a process the researchers compared to pushing a swing at the correct rhythm. While stronger tidal pulls resulted in faster events, the study also found that predictable tidal forces could lead to irregular, messy movement patterns. The authors suggest this model provides a framework for geologists to infer specific fault properties based on observed tidal triggering.