Large Earthquakes May Trigger Each Other on the Opposite Side of the World

Powerful earthquakes may trigger other large quakes even over great distances, according to a study published in the journal Scientific Reports.

Researchers from Oregon State University (OSU) analyzed seismic data from 1973 to 2016, finding that within three days of an earthquake of magnitude 6.5, others of magnitude 5.0 or larger were more likely to occur.

Furthermore, they showed that the region located on the opposite side of the Earth has the greatest chance of experiencing one of these induced earthquakes. An example of this link is the 1992, 6.7-magnitude earthquake in Indonesia which occurred 5.6 hours after a 7.7-magnitude earthquake off the coast of Nicaragua.

Until now, scientists thought that the only seismic activity a large earthquake could trigger were aftershocks—smaller magnitude quakes which result from the Earth's crust adjusting to the fault disturbance.

"Earthquakes are part of a cycle of tectonic stress buildup and release," Robert O'Malley, a researcher at OSU's College of Agricultural Sciences, said in a statement. "As fault zones near the end of this seismic cycle, tipping points may be reached, and triggering can occur."

When analyzing the data, the team looked at different earthquake cases to see whether large events were associated with the occurrence of subsequent quakes, taking care to filter out information regarding aftershocks to avoid anomalous spikes in the data.

"If large magnitude source events are the cause of triggering, then a measurable effect should be a systematic increase in the number of earthquakes that follow over baseline rates," the authors wrote in the study.

The test cases showed a clearly-detectable increase over the background rates. Furthermore, the team found that the higher the magnitude of earthquake, the more likely it is to be followed by another quake. It should be noted, however, that no direct link has been found between these quakes because current scientific knowledge cannot fully explain how this process would work.

"The understanding of the mechanics of how one earthquake could initiate another while being widely separated in distance and time is still largely speculative," O'Malley, said. "But irrespective of the specific mechanics involved, evidence shows that triggering does take place, followed by a period of quiescence and recharge."

According to the researchers, the latest results could help to improve earthquake forecasting in the short term and the creation of risk assessments.