This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: While not quite a fatal attraction, the gravitational pull of the moon and sun creates tiny stresses on Earth that can trigger events known as slow earthquakes. These are movements along fault lines (fault slips) that release their energy gradually over much longer periods than ordinary quakes.
Although they have been observed, exactly how these celestial bodies trigger them has been a relatively tough nut to crack. So a team of geoscientists led by Yishuo Zhou at PSL University in Paris created computer models of these fault lines to find out what is going on. To simulate a simplified fault, the researchers created a digital spring-block model in which a block slides along a fault while being pulled by a spring.
The idea was to make this virtual fault behave like the real Earth, so they programmed in well-established rules of friction that account for how rock strength changes when it moves or stays still. Then, they applied brief stress nudges and repeating wave-like forces designed to represent the sorts of tiny stresses produced by the gravitational pull of the sun and moon on Earth. The results revealed a fascinating pattern, as the research team details in their paper published in the Journal of Geophysical Research: Solid Earth.
Timing, force and friction were all key. In the simulations, small tidal pulls disrupted faults that would otherwise slide along steadily. The trigger occurred when the repeating pull of the sun and moon matched the rate at which the fault naturally responded to stress.
The fault's internal friction helps set that response rate and influences how it responds to stress. The fault could shift into a slow earthquake when timing, force and friction lined up. Stronger pulls produced faster events.
However, even smooth, predictable tidal forces sometimes created messy, irregular movement patterns. "Here, we show that even very weak tidal stresses can induce faults to slip through a process called resonance, much like pushing a swing at the right rhythm makes it move higher," wrote the scientists. Computer models simplify real-world conditions, so actual fault systems in nature might behave with far greater complexity.
Extract — continue reading at the source.
