Research team finds link between fault line slippage, large earthquakes

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Movement along fault lines may be a strong indicator of when large earthquakes will occur, according to a team of researchers from UC Berkeley and Japan.

In a report published in the journal Science on Friday, the team outlined its findings on how slow-slip events — movements between large tectonic plates — that occurred along a fault line approximately 1,000 kilometers long in Japan seemed to precede large earthquakes.

In Japan, tectonic plates press into one another, leading to slow-slips. This movement often results in small earthquakes and, as slow-slips accelerate, larger ones.

After analyzing 28 years worth of earthquake measurements, the team found that slippages between tectonic plates led to 6,125 earthquakes of magnitude 2.5 or greater.

The team discovered that slow-slips accelerate and decelerate periodically every one to six years. This cycle resembled the team’s observations of large earthquakes — those of magnitude 5 or greater — implying a possible connection between the two phenomena.

“It seems that slow slip events sometimes lead to large earthquakes,” said Professor Roland Burgmann, one of the report’s authors and a member of UC Berkeley’s seismology lab, in an email.

Burgmann also noted that a slow-slip acceleration preceded the magnitude-9 Japanese earthquake in 2011, which killed more than 15,000 people.

Although the team focused its research on earthquakes that occurred along the Japanese fault between 1984 and 2011, this work could potentially allow researchers to improve predictions of when earthquakes are likely occur, based on the periods of slow-slip events.

“This aspect of the science still has to be put to the test,” Burgmann cautioned in his email.

A lot of research on earthquake preparedness currently focuses on immediate warning systems such as ShakeAlert, a collaboration among UC Berkeley and several other institutions that uses the first few seconds of data from a large earthquake to warn residents of nearby endangered areas moments before the earthquake strikes in full force.

Unlike ShakeAlert, this report — which examined historical correlations between slow-slip acceleration and large earthquakes — could be applied to long-term earthquake preparedness.

The report, however, does not guarantee that an acceleration of plate slippage is a cause of large earthquakes.

“The real-time monitoring of slow-slip may help improve the probabilistic forecasts of future earthquakes,” said Naoki Uchida, one of the report’s authors and an assistant professor at Tohoku University in Japan, in an email.

Researchers cannot predict precisely when and where an earthquake will strike, but the team’s findings may allow them to narrow down time ranges in which large earthquakes may arise.

“We are just trying to better understand some of the underlying dynamics that determine when and where (large earthquakes) decide to strike next,” Burgmann said in an email.

Contact Maxwell Jenkins-Goetz at [email protected].