Can the Moon Cause Earthquakes?

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James O. Berkland is a Glen Ellen, California-based geologist and editor of Syzygy—An Earthquake Newsletter. He believes the gravitational tugs of the moon, sun, and other planets can influence earthquake activity. Berkland said he has accurately predicted tremors based on factors such as syzygy.

"Syzygy" refers to the alignment of three celestial objects. Syzygy of the sun, Earth, and moon occur twice a month, at the full and new moons. At such times, gravitational forces are at a maximum, especially when the bodies are close together, Berkland said.

The Earth and moon are closest together—at perigee—once a month. The Earth and sun are closest together—at perihelion—once a year. Perihelion currently occurs in early January. Maximum gravitation force occurs when a syzygy and perigee occur on the same day as perihelion.

According to Berkland, seismometers left on the moon by Apollo astronauts show that moonquakes occur most frequently at perigee.

"So we know Earth's gravity triggers moonquakes. I don't think any scientist disputes that," Berkland said. "When I learned that, I went to my former [U.S. Geological Survey] colleagues in Menlo Park [California] and pointed out this really exists, so what's so difficult about turning it around?"

According to Berkland, the U.S. Geological Survey said such a theory is ridiculous—the Earth is 82 times more massive than the moon. Though the Earth can trigger quakes on the moon, they said, the moon is too small to trigger any earthquakes.

But the moon is mostly solid and lacks a liquid core like the Earth, Berkland said. The Earth "is an active, living planet, and so it is not at all surprising that minor gravitational stresses can trigger earthquakes," he said.

Using syzygy and other factors—such as the number of cats and dogs listed in the lost and found in newspaper classified advertisements—Berkland said he accurately predicted several earthquakes, including the October 17, 1989 earthquake in San Francisco, California. Berkland said the number of cats and dogs reported missing goes up prior to an earthquake. The numbers went up significantly prior to the 1989 San Francisco quake, he said.

At least two major quakes may suppoort Berkland's theory. The December 26, 2004, magnitude 9.1 in Sumatra, Indonesia, occurred on the day of a full moon. Likewise, the March 27, 1964, magnitude 9.2 earthquake in Alaska occurred on the day of maximum high tide.

According to Berkland, such correlations are more than coincidences. They demonstrate a true connection between the moon and earthquake activity, he said.

But Bellini, the U.S. Geological Survey geophysicist, said, "There is still no known observation of an effect related to the moon and seismicity."

In a follow-up email to National Geographic News, Bellini questioned the scientific validity of Berkland's predictions. He said they appear to be "self-selected statistical analysis of historical seismicity rates and are so vague in time and location that they are certain to be correct."

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