Tuesday, August 29, 2017

Can Sun And Moon Trigger Quakes On Earth?

It was now about noon, and darkness came over the whole land until three in the afternoon, for the Sun stopped shining. And the curtain of the temple was torn in two.
Luke 23:44-45
In ancient times the sky was seen as sort of perfect clockwork. Stars and planet moved along fixed paths, repeating the same movements every year. Any changes in this apparent harmony, so it was believed, must also have effects on Earth.  A suddenly appearing comet, or moon and solar eclipses, were especially suspicious. Approaching comets were regularly suspected to cause earthquakes, especially large ones. The verse in the introduction maybe describes a solar eclipse, as the Sun disappears, and a following earthquake in biblical times. Still today, many believe that the position of Sun, Moon and even the other planets of our solar system, can cause earthquakes on Earth.
The Galileo spacecraft takes a beautiful image of the pale blue dot and its moon in December 1998. Source and Credit: NASA/JPL, Image in Public Domain.
Unfortunately (or maybe better so) the proposed mechanism can't work. The gravitational pull of the Sun and other planets, even of the largest one, is far too weak to cause an earthquake. It's insignificant if compared to the forces driving tectonics.

However, there seems to be some truth in the belief, that the Moon influences seismicity. Research published in 2016 suggests that some earthquakes are influenced by the Moon.  Studying the frequency of large quakes in Chile, California, and Japan, the researchers discovered, that quakes with a magnitude over 5 are more likely to occur during new or full moon when the Sun, Moon, and Earth align. The alignment, so the theory, pulls Earth's tides over the sea, changing the distribution of mass in an oceanic basin. The changed mass can put extra strain on fault systems located along the edges of continents, like the Cascadia region, the Andean subduction zone, and islands, like Japan. The faults are first compressed, like a spring, when the strain is released, the fault, now unclamped, is more likely to slip back, causing a quake.
The effect is, as even the researchers admit, extremely weak and acts more likely only on shallow faults. Only one in 10,000 quakes, occurring during a time of increased tidal stress, will be influenced and eventually grow significantly in magnitude. The primary causes of an earthquake, like tectonic movements, slow accumulation of strain, the resistance of rocks to deformation, friction and the presence of faults or layers of weak rocks, are by far the more important variables to consider when talking about earthquake risk. The Sun and Moon alone can't be used to foresee any earthquake.

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