What Moons, Tides and Earthquakes Have in Common

Image Courtesy of Wikimedia

Rishika Kenkre
Staff Writer

New research from Satoshi Ide, a seismologist at the University of Tokyo, concludes that huge earthquakes are more likely to occur during full and new moons when tidal stresses are the highest.

It was always known that Earth’s tides, phenomena resulting from a gravitational tug-of-war between the Moon and the Sun, put great stress on geological faults. Seismologists have generally agreed that the ocean’s twice-daily high tides can influence tiny, slow-motion tremors in certain places, including California’s San Andreas fault.

Although the details of how large earthquakes form and evolve have not been fully understood, the process is thought to involve a series of small ruptures cascading to create an extremely big one. Through this new research, researchers found that this cascade is more likely to occur during a full or new moon, when the Sun and Moon are exerting the maximum amount of pressure on the Earth.

To conduct their research, Ide and his colleagues looked at three separate earthquake records covering the entire world. For the 15 days leading up to each quake, the researchers allocated a number representing the relative tidal stress on that day, with 15 representing the highest. With this method, they found that large quakes, such as those that hit Chile and Tohoku-Oki, happened near the time of maximum tidal strain, or during new and full moons when the Sun, Moon, and Earth align.

In a sample of more than 10,000 earthquakes at around magnitude 5.55, an earthquake that began during a time of high tidal stress has a better likelihood to intensify to a magnitude of 8 or above. This is supported by examples such as the magnitude 9.3 Indian Ocean earthquake in 2004, the magnitude 8.8 Maule earthquake which hit Chile in 2010, and the magnitude 9.0 Tohoku-Oki earthquake which hit Japan in 2011. All of these earthquakes occurred near a time of sizable tidal stress, which is generally caused by full or new moons. The correlation between the high tidal stress and small earthquakes is still not present.

In 1925, a magnitude 6.8 earthquake caused extensive damage to the city of Santa Barbara. Dozens of buildings in downtown SB crumbled from the temblor. This major earthquake could be felt throughout Paso Robles, located in San Luis Obispo County, and as far south as Orange County. This earthquake took place a week after a new moon. Earthquakes and potential tsunamis are of concern to the University of California, Santa Barbara, which is just a few feet above sea level.

Ide states that this research should not change how societies should make preparations for potential earthquakes. He is currently looking at a list of earthquakes that occur where plates with oceanic crust slides under the continental crust, in order to see if his research can be supported by further evidence.