The Moon and Earthquakes

We all known that the moon is responsible for the Earth's  tides, which are strongest when the sun and moon are aligned, during a full moon or a new moon. That same pull of the moon is also affecting the earths crust.

[Foto: Nicolette van Berkel]

For years, scientists have speculated whether the moon might play a role in earthquakes. It would make sense that the moon’s gravity could tug at a fault in the crust, especially one that is already close to failing and slipping. But nobody had demonstrated firm evidence for this.

Studying data from the past two decades, researchers measured the timing of high tides and reconstructed the amplitude of the moon’s pull at those times, focusing on the two weeks prior to large earthquakes[1]. They measured the amplitude of the tides against the timing of those quakes, and found some of the largest and most devastating earthquakes in recent memory happened when the Earth’s crust was under the highest tidal stress. They found that very large earthquakes, including the 2004 Indian Ocean (magnitude 9,3 with tsunami), 2010 Maule earthquake in Chile (magnitude 8.8) and the 2011 Tohoku-Oki earthquake in Japan (magnitude 9.1 with tsunami), tend to occur near the time of maximum tidal stress amplitude.

The mechanisms underlying this connection are not entirely clear. The moon’s pull causes tidal disruptions that are far lower than those experienced in an earthquake. And not every change in tide comes with an earthquake and not every earthquake comes with a change in tide. Part of the problem is that scientists still don’t know exactly what causes a major earthquake. But one theory is that they begin as smaller fractures that build up via a cascading process, where the moon is constantly pulling.

Research also found that both small and major earthquakes are not always triggered by the moon[2]. But some of them might be, and so we’d do well to pay closer attention to the subtle yet powerful ways in which the moon exerts its influence on our planet.

[1] Ide et al: Earthquake potential revealed by tidal influence on earthquake size–frequency statistics in Nature – 2016. See here.
[2] Van der Elst et al: Fortnightly modulation of San Andreas tremor and low-frequency earthquakes in PNAS - 2016