Earthquakes can systematically trigger other ones on opposite side of Earth

Ring of Fire earthquake zone [image credit: BBC]

The understanding of the processes may be lacking, but the evidence is there according to researchers.

New research shows that a big earthquake can not only cause other quakes, but large ones, and on the opposite side of the Earth, reports ScienceDaily.

The findings, published today in Scientific Reports, are an important step toward improved short-term earthquake forecasting and risk assessment.

Scientists at Oregon State University looked at 44 years of seismic data and found clear evidence that tremblors of magnitude 6.5 or larger trigger other quakes of magnitude 5.0 or larger.

It had been thought that aftershocks — smaller magnitude quakes that occur in the same region as the initial quake as the surrounding crust adjusts after the fault perturbation — were the only seismic activity an earthquake could lead to.

But the OSU analysis of seismic data from 1973 through 2016 — an analysis that excluded data from aftershock zones — provided the first discernible evidence that in the three days following one large quake, other earthquakes were more likely to occur.

Each test case in the study represented a single three-day window “injected” with a large-magnitude (6.5 or greater) earthquake suspected of inducing other quakes, and accompanying each case was a control group of 5,355 three-day periods that didn’t have the quake injection.

“The test cases showed a clearly detectable increase over background rates,” said the study’s corresponding author, Robert O’Malley, a researcher in the OSU College of Agricultural Sciences. “Earthquakes are part of a cycle of tectonic stress buildup and release. As fault zones near the end of this seismic cycle, tipping points may be reached and triggering can occur.”

The higher the magnitude, the more likely a quake is to trigger another quake. Higher-magnitude quakes, which have been happening with more frequency in recent years, also seem to be triggered more often than lower-magnitude ones.

A tremblor is most likely to induce another quake within 30 degrees of the original quake’s antipode — the point directly opposite it on the other side of the globe.

Continued here.