EarthquakesQuestions raised about the predictive value of earthquake foreshocks

No one can predict when or where an earthquake will strike, but in 2011 scientists thought they had evidence that tiny underground tremors called foreshocks could provide important clues. If true, it suggested seismologists could one day warn people of impending temblors.

But a new study published in Nature Geoscience by scientists at Stanford University and Boğaziçi University in Turkey has cast doubt on those earlier findings and on the predictive value of foreshocks.

Stanford notes that the previous evidence came from a 7.6 magnitude earthquake in 1999 near Izmit, Turkey, that killed more than 17,000 people. A 2011 study in the journal Science found that the deadly quake was preceded by a series of small foreshocks – potential warning signs that a big seismic event was imminent.

“We’ve gone back to the Izmit earthquake and applied new techniques looking at seismic data that weren’t available in 2011,” said lead author William Ellsworth, a professor (research) of geophysics at Stanford School of Earth, Energy & Environmental Sciences. “We found that the foreshocks were just like other small earthquakes. There was nothing diagnostic in their occurrence that would suggest that a major earthquake was about to happen.”

“We’d all like to find a scientifically valid way to warn the public before an earthquake begins,” said co-author Fatih Bulut, an assistant professor of geodesy at Boğaziçi University’s Kandilli Observatory and Earthquake Research Institute. “Unfortunately, our study doesn’t lead to new optimism about the science of earthquake prediction.”

How do earthquakes begin?
Scientists including Ellsworth have proposed two ideas of how major earthquakes form, one of which – if scientists can detect them – could warn of a larger quake.

“About half of all major earthquakes are preceded by smaller foreshocks,” Ellsworth said. “But foreshocks only have predictive value if they can be distinguished from ordinary earthquakes.”