New Research In California Reveals Earthquakes Could Produce Greater Damage Than Previously Thought.

Scientists in California have found that earthquakes can occur much deeper below the Earth’s surface than originally believed, a discovery that alters their understanding of seismic behavior and potential risks.

Seismologists have long believed that earthquakes occur less than 12 to 15 miles underground in the planet’s brittle, rocky crust. But new research has found evidence of quakes deeper than 15 miles under the surface, in the upper mantle, an area where the rock is so hot that it is no longer brittle but creeps, moving around like an extremely hard honey. 

Three scientists at Caltech in Pasadena studied data collected over six months from 5,000 state-of-the-art sensors installed in Long Beach atop the Newport-Inglewood fault, one of the most dangerous in the Los Angeles Basin and which caused the magnitude 6.4 Long Beach earthquake of 1933.

Caltech seismology professor Jean Paul Ampuero, one of three authors of the study that was published Thursday in the journal Science, said the research raised the possibility that the Newport-Inglewood fault and others, such as the San Andreas, could see even more powerful earthquakes than expected. The earthquakes he and his colleagues studied were so deep that they were not felt at the surface by conventional seismic sensors.

The new report indicates that it’s possible a quake much closer to the surface could travel much deeper into the Earth, producing a stronger, more damaging rupture than previously believed was possible. 

“That got us thinking — that if earthquakes want to get big, one way of achieving that is by penetrating deep,” Ampuero said. “The big question is: If the next, larger earthquake happens, if it manages to penetrate deeper than we think, it may be bigger than we expect.”

It’s an idea that was first raised in 2012, also by Ampuero and several colleagues in the journal Science, when a magnitude 8.6 earthquake struck the Indian Ocean.

That was the largest quake of its kind “that has ever happened,” Ampuero said. It happened on a fault known as a “strike-slip,” the same kind of fault as Newport-Inglewood and California’s mighty San Andreas, the state’s longest fault.

But that Indian Ocean earthquake was so large, it was impossible to explain how it happened with existing science.

So answering the question of how an 8.6 earthquake occurred required a new explanation — that the quake occurred on a fault that not only ruptured the crust, but went deeper into the mantle.

If deep earthquakes can occur, researchers say, then it’s possible that the Newport-Inglewood fault — which runs under a densely populated swath of Southern California — could produce a larger earthquake that experts had believed possible. Scientists have longthought that the Newport-Inglewood fault could produce a temblor of up to magnitude 7.4.

But a lot more study needs to be done.

The deep quakes that the Caltech scientists detected were only microquakes — topping out at about a magnitude 2.

Therefore, it is also possible that these deep earthquakes remain small and don’t help a larger earthquake closer to the surface become stronger. With this theory, earthquakes in this deep zone occur in small pockets far away from one another and don’t link in a way that allows a big earthquake to get stronger.

“This could be good news, in a way, because if they never break together, that means they can break in tiny earthquakes, but they cannot break in large ones,” Ampuero said. “So several questions are still open. I wouldn’t say that this is cause for alarm at this point. These are very interesting questions that we need to pursue.”