The study, published in the journal ‘Nature Geoscience’ and conducted by a team from the University of Tokyo, argues that the same gravitational influence that the moon has on the oceans may also trigger earthquakes along Earth’s most fragile fault lines. The research team calculated the levels of ‘tidal stress’ before major earthquakes of the last few decades and found that high levels of stress were often followed by major quakes.
Satoshi Ide and his colleagues investigated three separate earthquake records covering Japan, California and the entire globe. For the 15 days leading up to each quake, they assigned a number representing the relative tidal stresses on that day, with 15 representing the highest. They found that large quakes, including those that hit Chile and Tohoku-Oki occurred near the time of maximum tidal strain, during new and full moons when the Sun, Moon and Earth align. For more than 10 000 earthquakes of around magnitude 5.5 on the Richter scale, the researchers found, an earthquake that began during a time of high tidal stress was more likely to grow to magnitude 8 or above. However, they found no correlation between smaller earthquakes and tidal stress.
‘This suggests that the probability of a tiny rock failure expanding to a gigantic rupture increases with increasing tidal stress levels,’ the scientists wrote in ‘Nature Geoscience’. ‘We conclude that large earthquakes are more probable during periods of high tidal stress.’
The research team also argue that the 9.1 magnitude 2004 Boxing Day earthquake that caused an immensely destructive tsunami which killed around 230 000 people across the Indian Ocean was also likely precipitated by the influence of the moon. So was the 2011 quake that hit the east coast of Japan which left around 15 000 people dead and caused a major nuclear incident at the Fukushima plant.
In the same way in which Earth’s tides are caused by the gravitational pull of the moon as it moves over the planet’s surface, the moon also exerts subtle pressures on the Earth’s crust, causing occasional buckles. When this slight buckling occurs around an already fragile fault line, it may set off cascading reactions that result in a major earthquake.
Ide and his team argue that their findings could allow for better earthquake forecasting and help societies to prepare for possible quakes, particularly with regards to large ones, through the development of new monitoring systems that take the influence of the moon as a guiding factor.
However, the connection still needs to be fully verified, with other seismologists pointing out that many large earthquakes of the last decade have occurred at a time when tidal stress wasn’t a major precipitating factor. Indeed, the study will not put the question to a final rest. There are just too many factors that contribute to the triggering of an earthquake.
Ide and his team are now looking at an additional list of earthquakes that occur where tectonic plates with oceanic crust plunge beneath continental crust to see if their recorded pattern also holds up there as well.
Source: Based on information from CORDIS