Megaquakes could be far more powerful than thought: Researchers find quakes can occur more than 15 MILES beneath California

• e-mail

Scientists in California have discovered evidence of earthquakes more than 15 miles beneath Earth’s surface, shaking up previous understanding on seismic behaviour.

Long-held beliefs have suggested that quakes happen at much shallower points, less than 12 to 15 miles deep, and are confined to the crust.

Now, researchers have found that the Newport-Inglewood fault, a major formation that spans the Los Angeles basin, is ‘seismically active down to the upper mantle.’

The discovery indicates that deeper, more powerful earthquakes than expected could be within the realm of possibility for this fault and others, including the fearsome San Andreas.

Researchers have found that the Newport-Inglewood fault, a major formation that spans the Los Angeles basin, is ‘seismically active down to the upper mantle.’ This is said to be one of the most dangerous faults in the Los Angeles Basin

In a new study published to the journal Science, scientists at the California Institute of Technology analyzed data from 5,000 sensors on the Newport-Inglewood fault in Long Beach.

This is said to be one of the most dangerous faults in the Los Angeles Basin, according to the LA Times.

Examining data collected over six months, the researchers discovered a series of small, deep quakes occurring in the upper mantle, a hot, slow moving region beneath the crust.

While it was previously thought impossible for earthquakes to occur in this area, the researchers say the Newport-Inglewood fault appears to extend into the mantle. 

Examining data collected over six months, the researchers discovered a series of small, deep quakes occurring in the upper mantle, a hot, slow moving region beneath the crust. Previously, it was thought to be impossible for earthquakes to occur here

So far, those observed deep below the surface were just microquakes, at a maximum magnitude of 2.

But, if an earthquake near the surface could travel much deeper, the researchers say it might be able to produce a much more devastating event.

‘That got us thinking – that if the earthquakes want to get big, one way of achieving that is by penetrating deep,’ Jean Paul Ampuero, one of the authors of the study, told the Times.

‘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.’

The discovery indicates that deeper, more powerful earthquakes than expected could be within the realm of possibility for this fault and others, including the fearsome San Andreas, pictured in the Carrizo Plain

This could reveal the mechanisms behind massive earthquakes, such as the 8.6 magnitude event that struck the Indian Ocean in 2012, which have been too large to be explained with current understanding, the LA Times reports.

That particular quake occurred along a strike-slip fault – the same kind which makes up the Newport-Inglewood fault and the San Andreas, which has long provoked fears of 'The Big One.'

Researchers say a deep earthquake along the Newport-Inglewood fault could make for a much more powerful event than expected, which already ranges from a probable magnitude of 6.0 to 7.4.

But, they say far more research is needed to determine if this is case.

The researchers say it also could be possible that the deep earthquakes remain small and isolated, preventing them from strengthening a big earthquake.

And, as those found were all within a 9-square mile beneath Long Beach, they say these events may have been an anomaly specific to this area.

This comes just days after researchers revealed a newly discovered fault line running parallel to the San Andreas fault in Southern California.

The new Salton Trough Fault, which runs parallel to the San Andreas Fault, could impact the earthquake-prone region that includes the greater LA area, seismologists say. It is in an area where a swarm of nearly 200 small earthquakes hit last week, raising concerns they might trigger a larger earthquake on the southern San Andreas Fault

The new Salton Trough Fault, which runs parallel to the San Andreas Fault, could impact current seismic hazard models in the earthquake-prone region that includes the greater Los Angeles area, seismologists say.

The newly identified strike-slip fault within the Salton Sea, just west of the San Andreas Fault, is in an area where a swarm of nearly 200 small earthquakes hit last week, raising concerns they might trigger a larger earthquake on the southern San Andreas Fault. 

PLANS FOR THE 'BIG ONE' 

Federal, state and military officials have been working together to draft plans to be followed when the 'Big One' happens.

These contingency plans reflect deep anxiety about the potential gravity of the looming disaster: upward of 14,000 people dead in the worst-case scenarios, 30,000 injured, thousands left homeless and the region's economy setback for years, if not decades.

Julian Lozos, an assistant geophysics professor at California State University, claimed there is a strong chance this quake will coincide with one along the adjacent San Jacinto fault line, which runs through more heavily-populated cities. Both fault lines are shown above

As a response, what planners envision is a deployment of civilian and military personnel and equipment that would eclipse the response to any natural disaster that has occurred so far in the US.

There would be waves of cargo planes, helicopters and ships, as well as tens of thousands of soldiers, emergency officials, mortuary teams, police officers, firefighters, engineers, medical personnel and other specialists.

'The response will be orders of magnitude larger than Hurricane Katrina or Super Storm Sandy,' said Lt. Col. Clayton Braun of the Washington State Army National Guard.