From the news: Evidence that tidal forces influence earthquakes

Large earthquakes can have immense impacts on humankind, killing thousands of people and creating widespread devastation. While decades of research have helped us understand an earthquake’s complex processes, predicting earthquakes remains a scientific dream.

However, a new study in Nature Geoscience may help us begin to make that dream a reality. “Earthquake potential revealed by tidal influence on earthquake size-frequency statistics” by Ide et al. (2016) provides evidence that large earthquakes are more likely to occur during times of high tidal stresses that affect the Earth’s crust.

Ocean tides are the result of the Moon’s gravity pulling on the ocean as it travels around the Earth. The moon also pulls the surface of the Earth toward it, creating a solid earth tide. These solid tides raise and lower the Earth’s surface imperceptibly over a period of twelve hours, so we cannot see them without scientific instruments.

However, these small ocean and earth tidal stresses may have significant effects. To analyze these effects, Ide et al. looked at the relationship between the amplitude of tidal stresses during large earthquakes. Several large earthquakes occurred during periods of high amplitude tidal stresses, including the 2004 Sumatra earthquake, the 2010 Maule earthquake, and the 2011 Tohoku-Oki earthquake. Ide et al. also found several large earthquakes that did not occur during these periods of high tidal stress.

To examine this relationship more closely, Ide et al. looked at more than 10,000 earthquakes worldwide with magnitudes greater than 5.5 and found that a greater number of large earthquakes occur when tidal stresses are high. Ide et al. interpret this to be the result of high amplitude tidal stresses causing small fractures to rupture into large fractures, turning small earthquakes into large earthquakes. According to Ide et al., a M5 earthquake is six times more likely to become a M9 earthquake during times of high tidal stresses.
                  Further study is needed to verify the causal interpretation of Ide et al. and to more fully understand the implications of this study. But if a causal link is found behind the statistical correlation of large earthquakes and high amplitude tidal stresses, this study could be instrumental in building an earthquake prediction model.

Read the paper at: Ide, Satoshi, Suguru Yabe, and Yoshiyuki Tanaka. "Earthquake potential revealed by tidal influence on earthquake size-frequency statistics." Nature Geoscience (2016) http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2796.html