13 Sep 2016

Earthquakes linked to tide and moon phases

1:58 pm on 13 September 2016

A study by Japanese researchers has linked the timing of large earthquakes with tidal stresses around the time of a new or full moon.

Sea and moon

Photo: 123rf

Research conducted by University of Tokyo academics and published in the journal Nature Geoscience examined the tidal activity prior to large earthquakes around the world during the last 20 years.

The study looked at earthquakes of magnitude 5.5 or higher, including the magnitude 9 earthquake that struck Japan in March 2011, triggering a devastating tsunami.

It said some of the biggest quakes occurred when tidal stresses were high, at spring tides, just after a new or full moon.

Victoria University geophysicist John Townend said the research did not mean people could predict when and where a big earthquake was likely to strike.

"This analysis suggests that there is some relationship between tidal cycles and the likelihood of a big earthquake," he said.

"But it's really very non-prescriptive in terms of which particular tidal cycle is going to trigger an earthquake, and where in the world that's going to be, and how big that earthquake might be.

"It's important not to forget that the timing of earthquakes, in spite of this research, remains largely unpredictable, and therefore we need to put a lot of effort into being prepared and taking the appropriate measures to ensure that - when an earthquake does occur - our society and our infrastructure and people are as prepared as possible."

The study did not find any clear correlation between tidal stress and small earthquakes.

Dr Townend said there had long been theories about the relationship between tides and earthquakes, and this research helped clarify that.

Devastation in the city of Ofunato, Japan, on March 15, 2011, four days after the earthquake

Devastation in the city of Ofunato, Japan, on 15 March 2011, four days after the magnitude 9 earthquake and tsunami. Photo: AFP

Get the new RNZ app

for ad-free news and current affairs