Scientists detect a strange "wobble" before two major earthquakes

An international team of experts has identified changes in Earth’s surface that occurred months before two major earthquakes. The ground underwent a shift, or a “wobble,” that may be used to help experts predict future earthquakes.

The 2011 earthquake off the Pacific coast of Tōhoku, often referred to as the Great East Japan Earthquake, had a magnitude of 9.0. The quake triggered massive tsunami waves that killed more than 15,000 people and destroyed 450,000 homes.    

In the new study, scientists analyzed data from Japan’s large network of earthquake monitoring equipment. They detected a strange movement in the ground that shifted the country’s landmass from side to side, and this wobbling motion lasted for up to seven months. 

The study revealed that Japan was shifting from west to east and back again by a fraction of an inch per month leading up to the earthquake. 

While these tiny shifts were “imperceptible,” the researchers found them to be obvious in data that was collected from more than 1,000 GPS stations around the country.

Study co-author Dr. Michael Bevis is a professor of Geodynamics in the School of Earth Sciences at The Ohio State University. Dr. Bevis said what they found in Japan was an enormous but very slow wobble, something that had never been observed before.

“The world is broken up into plates that are always moving in one way or another. Movement is not unusual. It’s this style of movement that’s unusual,” said Dr. Bevis.

The wobble could indicate that in the months before the earthquake, the plate under the Philippine Sea began a “slow slip event,” said Dr. Bevis. He explained that the catalyst for the 2011 quake was a relatively gentle underthrusting of two oceanic plates beneath Japan.

Study lead author Dr. Jonathan Bedford is a researcher at the GFZ German Research Centre for Geosciences. He noted that the findings cannot be applied to other vulnerable subduction zones that lack the monitoring capabilities of Japan’s advanced network.

When the researchers analyzed data from the 2010 Maule earthquake in Chile, which had a magnitude of 8.8, they detected a similar wobble. 

Dr. Bedford said the data was just good enough to capture the signal.

“We really need to be monitoring all major subduction zones with high-density GPS networks as soon as possible,” he added.

The team hopes that future wobbles could serve as early warning signs of upcoming disasters.

Study co-author Dr. Marcos Moreno Switt from Universidad de Concepción said that satellite data makes it possible to identify how the Earth’s surface changes before major earthquakes. 

“The vast majority of major earthquakes are likely to be accompanied by precursor activity, as had already been recorded before the Iquique earthquake in 2014, and now before the 2011 Japan and Maule earthquakes in 2010,” said Dr. Switt.

“Much remains to be understood. this pioneering activity, but it is a great advance to be able to detect these movements. This is the focus of our new RING 2020 PRECURSOR project, financed by Anid, in which we will integrate an interdisciplinary team of Chilean and foreign researchers to obtain more and better information on these processes.”

The study is published in the journal Nature.

—

By Chrissy Sexton, Earth.com Staff Writer