Data point to possibly greater quake risk

“The opinion piece calls out for more effort to really try and understand both where supershear ruptures are likely to occur and the implications,” Aagaard said.

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AN AERIAL view shows a creek in Santa Margarita, Calif., altered by the San Andreas fault, which could be at risk for supershear quakes.

(DAVID MCNEW Getty Images)

The idea that the rupture on a fault can move even faster than the seismic shear wave was theorized as early as the 1970s, said Elbanna, who is set to become director of the Statewide California Earthquake Center next year.

But by the turn of the century, there had been only one earthquake globally that some scientists suspected was a supershear event — the magnitude 6.4 Imperial Valley earthquake in 1979.

It was only in the late 1990s that the idea of supershear earthquakes began to be taken more seriously. Lab experiments at Caltech showed they were physically possible.

And in the last quarter-century, a growing number of earthquakes of magnitude 7 or greater have been determined to be supershear, observations that have been assisted by the installation of monitoring devices around the world.

A key breakthrough came during the magnitude 7.9 earthquake in Alaska in 2002, where a sensor station happened to be close enough to the ruptured Denali fault to record data confirming what scientists would expect from a theoretical supershear earthquake, Elbanna said.

Since then, scientists have identified more earthquakes as such events.

“We're getting better data, and so now we see this,” said seismologist Lucy Jones, a Caltech research associate.