THE Earth’s solid surface, like the oceans, gets deformed by the gravity of the moon and the sun. Geologists have long wondered whether this can lead to earthquakes, and now they finally have an answer.
Besides causing ocean tides, the sun and the moon also pull at the Earth’s crust and upper mantle, resulting in daily “Earth tides”. At its strongest, this pull can ease enough of the pressure on the tectonic plates for them to slip past each other. But these stresses are about a thousand times weaker than those created by the normal movement of tectonic plates, so it has been difficult to link seismic activity to peak tides.
To see if there is a connection, of the National Geographic Institute in Paris, France, and his team analysed records of more than 400,000 earthquakes, 10 times as many as any previous study. They found that about 1 per cent of earthquakes do coincide with Earth tides (Earth and Planetary Science Letters, ). “It’s small, but since we used such a large database there’s just a tiny chance it could have arisen from random variation,” says Metivier.
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