Moon's gravity linked to earthquakes

The moon's gravity apparently triggers some earthquakes that occur on the borders of techtonic plates, a team of scientists revealed in the online version of Science magazine.

The study, carried out by Sachiko Tanaka at the National Research Institute for Earth Science and Disaster Prevention in Ibaraki Prefecture and others, is the first of its kind in that it explains the relationship between the moon and earthquakes.

Tanaka and other researchers analyzed earthquakes with a scale larger than magnitude 5.5 that occurred around the world on the borders of techtonic plates from 1977 to 2000.

Their research and analysis shows that earthquakes, coupled with shifts in the faults, often occurred at a time when the moon's gravity and earth's tides jointly helped such plates move.

In particular, more than 70 percent of the 250 strongest earthquakes followed this pattern of plate movement with the assistance of the moon's gravitation and earth's tides.

About 1 in 1,000 of the forces that constantly pressure the earth's plates is caused by the moon's gravitation, and this could be the final factor in triggering earthquakes, the researchers said.

"If we investigate the connection between the moon's gravitation and small-scale earthquakes that occur in areas where a large-scale tremor is feared to hit, we may be able to predict large quakes," Tanaka said. (Mainichi Shimbun, Japan, Oct. 22, 2004)