Could we have seen it coming? (Image: Aflo/Rex Features)

THE rise and fall of the tides could help us to predict major earthquakes like the magnitude 9 quake that triggered Japan’s tsunami last year.

Sachiko Tanaka of the National Research Institute for Earth Science and Disaster Prevention in Tsukuba, Japan, says that as stresses build up in the Earth’s crust, it becomes more susceptible to minor earthquakes triggered by tidal forces, a sign of major quakes to come. She has spent over a decade amassing evidence for her theory. According to her latest results, tidally triggered earthquakes were rife off the north-east coast of Japan for several years before 2011’s massive earthquake.

“I read hundreds of earthquake prediction papers,” says Ross Stein of the United States Geological Survey in Menlo Park, California. “The vast majority is dry rot. Tanaka’s stands out. It could be very important.”


At high tide, more water is piled up on top of geological faults, adding to the stress acting on the rocks. If the fault is already close to rupture, the effect can trigger small tremors.

Tanaka compared records of tides and submarine earthquakes from 1976 to 2011 for 100,000 square kilometres surrounding the epicentre of last year’s quake. For the first 25 years of records, there was no sign of tidally triggered earthquakes, but after 2000 the number of these quakes gradually increased, reaching a peak just before last year’s megaquake. Afterwards, the effect disappeared again (Geophysical Research Letters, DOI: 10.1029/2012GL051179).

Tanaka’s findings show that stress was building up in the region for a decade before the main quake struck. Her earlier research had uncovered a similar effect in the run-up to three Sumatran earthquakes, including the 2004 quake that caused the Boxing Day tsunami. Tidal quakes happened more frequently in the run-up to bigger quakes, suggesting stress had built up year-on-year.

Despite decades of effort, seismologists still cannot reliably predict earthquakes. Tanaka’s approach is promising, but Harold Tobin of the University of Wisconsin-Madison points out that her analysis was done after the quake happened.

Tanaka is cautious, but will now try predicting quakes. “I am planning to monitor tidal triggering in the north-eastern Japan and Sumatra subduction zones,” she says.

“Just for something to have this level of promise is unique,” says Stein.