Tidal Seismicity in the Moon and Implications for the Rocky Interior of Europa

Abstract

Seismology is a powerful tool for probing the deep interiors of planetary bodies. Just as deep moonquakes triggered by Earth’s tides occur on the Moon, as observed by the Apollo seismometers, icy moons of the giant planets may also have seismically active deep interiors, opening up future prospects for in situ seismic investigations at their surfaces. Of notable interest is Jupiter’s moon Europa, with its dynamic ice shell and potentially habitable subsurface ocean. In this work, we use different interior models of the Moon and model the tidal stress inside them to determine the most likely times and locations for the triggering of tidal moonquakes. Using the Mohr–Coulomb failure criterion, we derive cohesion and friction values for the lunar interior to match the observations of deep moonquakes by Apollo at a depth between 700 and 1200 km. By extending the same approach to different interior models of Europa, we show that Europa quakes triggered by the tides of Jupiter are 10 times more likely to occur than tidal moonquakes. The strength and depth of these tidal Europa quakes (euroquakes) strongly depend on the interior structure, with stronger events at the core–mantle boundary for liquid core models, while solid core models can be more prone to failure at the bottom of the ocean floor. Models without a metallic core favor failure in the upper third of the mantle with event strength similar to that in the solid core models.

Predicting Deep Moonquake Source Regions Using Their Temporal and Spatial Patterns and Machine Learning

“…However, the real causes of their origins are yet to be discovered. There are still significant puzzles about their origin, as cyclic tidal stresses, caused by the monthly motion of Moon around Earth, are far less than the estimated confining pressures where DMQs occur (Cheng & Toksöz, 1978;Minshull & Goulty, 1988) suggesting extremely low cohesion and friction values if a Mohr-Coulomb failure model is used (Pou et al, 2024). This opens the question of whether we need both tectonic and ambient tidal stresses to explain their mechanical origin (Frohlich & Nakamura, 2009).…”