THE Earth鈥檚 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鈥檚 crust and upper mantle, resulting in daily 鈥淓arth tides鈥�. 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, ). 鈥淚t鈥檚 small, but since we used such a large database there鈥檚 just a tiny chance it could have arisen from random variation,鈥� says Metivier.
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