The fault that triggered a magnitude 8.2 quake off the northern Chilean coast was overdue for a significant earthquake, and an even more powerful temblor could be in store, said Rick Allmendinger, a Cornell University professor of earth and atmospheric sciences.
"This segment in Chile had not broken since 1877," said Allmendinger, a geology expert who has extensively studied the northern Chilean fault zone. "It had been quiet for an unusually long period of time."
But the 8.2 earthquake, which seismologists said struck about 950 miles north of Chile's capital, Santiago, wasn't powerful enough to release all the friction that had been built up in this zone, where the Nazca plate is sliding underneath the South America plate, Allmendinger said.
"It's probably not big enough to have released all of the energy that had been stored up along that locked plate boundary for the last 140 years or so," Allmendinger said. "Is this the Big One for that area? Or was it a foreshock to a presumably an even bigger earthquake?"
Scientists can't predict earthquakes, although there has been a pattern of smaller earthquakes preceding a magnitude 9.0
For instance, Allmendinger said, there were strong earthquakes before the world's most powerful temblor on record, a 9.5 earthquake off southern Chile in 1960 that killed thousands and sent damaging tsunami to Haiwaii, Japan, the Philippines and the U.S. West Coast.
And before the 2011 Japan tsunami, there was a magnitude 7.3 earthquake that turned out to be a foreshock of the magnitude 9.0 earthquake.
In the two weeks before Tuesday's magnitude 8.2 quake, scientists such as Allmendinger had been studying a cluster of earthquakes off northern Chile that "have been similar to those that appeared prior to the Tohoku [Japan] earthquake."
A 6.7 temblor struck that area off the Chilean coast on March 16.
"We're hoping for the sake of all of our friends in northern Chile that this is the Big One and there isn't another Big One coming. We're keeping our fingers crossed at this point," Allmendinger said in an interview from Ithaca, N.Y.
Subduction zone earthquakes, like the one that triggered Tuesday's temblor, cause the world's most powerful earthquakes, unleashing more energy than the San Andreas could in California.
They are so powerful because, unlike the San Andreas, which is essentially a vertical fault, subduction zone earthquakes occur on a plane that's at a low angle, as one piece of Earth's crust slides underneath another, Allmendinger said.
That low angle means there is much more surface area of the fault to slip in the underground "seismogenic" zone that causes earthquakes.