Big quakes more likely during spring tides - study

Damage following Japan's massive quake in 2011 (Reuters)
Damage following Japan's massive quake in 2011 (Reuters)

Big earthquakes are more likely to strike at spring tides, when the moon is new or full, new research has found.

And Ken Ring, the alternative weather predicter who faced widespread ridicule in 2011 for claiming he predicted the Christchurch quakes using the moon, says it's "long overdue" that science caught up.

Researchers at the University of Tokyo say some of the biggest quakes to strike the world in the last two decades came when tidal stresses were high. The tides are caused by the gravitational pull of the moon and sun.

"Tectonic tremors deep within subduction zones are highly sensitive to tidal stress levels, with tremor rate increasing at an exponential rate with rising tidal stress" the study, published Nature Geoscience, reads.

Notable quakes that happened during these times of high tidal stress include the 9.3 magnitude Sumatran quake of 2004 and the 8.8 Chile quake in 2010.

The researchers didn't find any causal link between small quakes and the moon. But quakes measuring 5.5 or greater were more likely when the moon was full or new, suggesting quakes that would have been small can be turned into big ones.

"I was scolded for saying that very thing back in 2011," says Mr Ring. "As far as I'm concerned it's welcome news and I totally agree."

King tides are when spring tides coincide with the moon's closest approach to the Earth, and Mr Ring says this is when earthquakes are most likely to happen.

He says mainstream geologists took a long time to figure this out because "they haven't been trained in any of the moon science".

"They just declare because it's not in their training it can't be important, and therefore it must be wrong. Unfortunately it becomes less than science at that moment.

"Science must always be open-minded, must always embrace new ideas. It was always the mavericks that changed progress in science."

Government-owned GNS Science declined to comment on the findings, but University of Melbourne quake expert Mark Quigley has his doubts, calling them "nice theories" with little practical use.

For example, the magnitude 9 Tohuku quake of 2011 which caused a tsunami and the Fukushima nuclear disaster, happened at "exactly the opposite" time the research predicts - halfway between the new and full moons.

"I am not saying that tidal stresses are unimportant things to consider within the variety of processes that may influence earthquake behaviour," says Assoc Prof Quigley.

"But when we consider how such a phenomenon could be practically considered within a coastal hazard perspective, what is the recommendation here? That we stay away from beaches close to subduction zones on full moons? This certainly would not have helped in the Tohoku example."

He says a 7.2 quake which struck two days before the big one would have put much bigger stresses on the plates than any tidal influences. This quake also didn't line up with the researchers' predictions.

"Many countries like Japan have earthquake early alarm systems, seismic building codes, well-engineered sea walls, and evacuation strategies in place; these are the measures that help to reduce seismic and tsunami risk."