Big quakes systematically trigger others in the Earth's other hemisphere: Study

The findings help scientists better conduct earthquake forecasting and risk assessments.

Researchers at Oregan State University have shown that big earthquakes can do more than just cause other, smaller tremors. They can also cause much larger quakes in the other hemisphere, according to a study reviewing the biggest earthquakes in history.

Seismic data over 44 years was processed by the scientists, who saw clear evidence for their theory about earthquakes with a magnitude of 6.5 or higher triggering other quakes that were 5.0 or higher elsewhere.

So far, aftershocks from earthquakes have been thought to happen in areas close to where the initial quake occurs — as the crust adjusts to the newly created fault lines around the epicentre.

These aftershocks, along with smaller quakes that happen at great distances from the epicentre, were the only global phenomena geologists knew resulted from large earthquakes.

A figure from the study showing areas of maximum impact after a large source quake. Source: Nature Reports

The analysis of seismic events from 1973 to 2016 in the study was done differently than previous research of a similar nature — they removed aftershocks from consideration and extended the time window of any resulting quakes that might have occurred as a result.

It was evident to the researchers from their data that other earthquakes appeared far more likely for up to three days following a large earthquake.

They also found that higher magnitude quakes, which seem to have occurred more frequently in recent years, are more likely to trigger other quakes in a 30-degree range of the original quake's antipode (the point directly opposite it on the other side of the globe).

“The understanding of the mechanics of how one earthquake could initiate another while being widely separated in distance and time is still largely speculative,” said Robert O’Malley, lead author of the study, to university press. “But irrespective of the specific mechanics involved, evidence shows that triggering does take place, followed by a period of quiescence and recharge.”

The findings, published on 2 August in Nature Scientific Reports, help scientists better conduct earthquake forecasting and risk assessments.

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