Does the moon influence quakes? Scientists study the relationship

THE Earth has been around for roughly 4.6 billion years, yet its various phenomena have left many scientists puzzled.

For one, earthquakes have been of great interest for scientists, as various evidence of forces that have triggered these natural occurrences are slowly being uncovered throughout time and based on data collected.

This past week a deadly 7.8-magnitude earthquake hit New Zealand and has caused a reported 2-meter lift on its seabed with a tsunami warning.  According to New Zealand’s official source of geological hazard information, GeoNet, “multiple faults have ruptured,” indicating a slip of the Kekerengu fault, a new fault at Waipapa Bay, a movement on the Hope fault and the Hundalee fault.

Coincidentally, the supermoon also occurred on the same day the earthquake happened. It is yet the biggest supermoon in 68 years.

For Filipinos, the supermoon was gazed upon the night of November 14, while in New Zealand, its peak appeared after midnight of November 15.

This supermoon is the closest encounter between the moon and the Earth with a distance of 356,509 kilometers.

It will not be as close until November 25, 2034, although other supermoons will come in between these years.

The supermoon last Monday appeared as much as 14 percent larger in the sky and 30 percent brighter to human vision.

Tidal waves, stresses

Nonetheless, the moon causes stronger tidal waves and stresses. According to Filipino astrophysicist Dr. Rogel Mari Sese, “Earth’s tides are caused by the gravitational forces of the sun and moon.”

In an interview with the BusinessMirror, he said: “Since the force of the sun’s gravity is smaller compared to the moon’s, the moon causes a stronger disruption of the waters on Earth, hence, the tides as its effect.”

Although it has long been debated if the effect of the moon’s gravity on Earth, such as tidal stresses, can cause stronger earthquakes, some scientists were curious enough to investigate on whether the tidal stresses caused by the moon can affect more than just the Earth’s waters.

In a recently published article from the journal Nature Geoscience written by scientists Satoshi Ide, Suguru Yabe and Yoshiyuki Tanaka, entitled “Earthquake potential revealed by tidal influence on earthquake size-frequency statistics,” they concluded that large earthquakes are more likely to happen when tidal stress is high.

Ide and Yabe, from the Department of Earth and Planetary Science, and Tanaka from the Earthquake Research Institute, all from the University of Tokyo, gathered data from global, Japanese and Californian earthquake catalogues. Based on their research, very large earthquakes occur near the moments of maximum tidal stress caused by the moon.

In their research, they found out that earthquakes were more evident when the tides are stronger and create pressure.

“We find that very large earthquakes, including the 2004 Sumatran, 2010 Maule earthquake in Chile and the 2011 Tohoku-Oki earthquake in Japan, tend to occur near the time of maximum tidal stress amplitude,” the published paper said.

The 2004 Sumatran earthquake was recorded at 9.1 magnitude, 2010 Maule earthquake  had an 8.8 magnitude and the 2011 Tohoku-Oki earthquake in Japan also ha d a 9.1 magnitude.

All of these earthquakes and their tidal stresses were carefully investigated 30 days before and after the tremors.  “In particular, a clear causal relationship between small earthquakes and the phase of tidal stress is elusive,” the team’s paper said.

However, they still concluded based on their outputs that the relationship is reasonable.

“This suggests that the probability of a tiny rock failure expanding to a gigantic rupture increases with increasing tidal stress levels.”

Although the research might prove to be rational, it is not reliable for predicting such events. According to New Zealand’s GeoNet web site, “In large groups, earthquakes exhibit slight associations with lunar cycles,  but this is not reliable for forecasting.”

It said that New Zealand has two tides a day and there is no clear connection in location. “The occurrence of the full moon around the globe does not allow us to say how big, when and where any earthquake might be.”


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