Breakthrough in earthquake prediction as scientists find big quakes follow a ‘silent slip’
- Researchers placed 55 seismometers along the ocean floor off the West Coast
- This allowed them to collect data on over 1,600 earthquakes along Blanco fault
- The team found shallow mantle creep and seismic swarms preceded big quakes
Scientists in Oregon have identified new clues on the warning signs of a big earthquake.
A new study has found that large quakes tend to follow two types of activity: shallow mantle creep and seismic swarms.
The team used 55 seismometers placed on the bottom of the Pacific Ocean near the Blanco fault to track more than 1,600 earthquakes in the region over the course of a year.
According to the team, the findings could also help to explain the so-called ‘silent slip’ that occurs along a fault even when no earthquake activity is detected.
Scroll down for video
The so-called silent slip occurs in a region between the crust and the upper layer, called the Moho, the researchers say. ‘We see slow, aseismic slips that occur at depth in the fault beneath the Moho and load the shallower part of fault,’ according to the researchers. This is illustrated
Silent slip, also known as slow slip, is a type of aseismic slip.
‘Slow slip directly triggers seismic slip – we can see that,’ said co-author and grad student, Vaclav Kuna.
‘The findings are very interesting and may have some broader implications for understanding how these kinds of faults and maybe other kinds of faults and maybe other kinds of faults work.’
The researchers from Oregon State University collected data from September 2012 to October 2013 near a 130-kilometer (80 miles) stretch of the Blanco fault known as Blanco Ridge.
The ridge has two ‘rough edges’ that produce earthquakes around magnitude 6 every 14 or so years.
‘It’s a very seismically active fault that generates significant earthquakes at higher rates than the majority of faults on land, making it ideal for studying the process of earthquake generation,’ Kuna said.
‘Our work was enabled by recent advances in long-term ocean-bottom seismometer deployments and is only the second major project targeting an oceanic transform fault,’ said co-author John Nabelek, professor of geology and geophysics at OSU.
According to the researchers, activity at the Blanco fault could directly tie into ‘the Big One.’
The fault sits near the Cascadia Subduction Zone, which predicted to be capable of producing a magnitude 9 or bigger earthquake in the foreseeable future.
The team used 55 seismometers placed on the bottom of the Pacific Ocean near the Blanco fault to track more than 1,600 earthquakes in the region over the course of a year. The Blanco fault is illustrated above
‘The Blanco fault is only 400 kilometers offshore,’ Nabelek said.
‘A slip on Blanco could actually trigger a Cascadia Subduction slip; it would have to be a big one, but a big Blanco quake could trigger a subduction zone slip.’
The so-called silent slip occurs in a region between the crust and the upper layer, called the Moho, the researchers say.
‘We see slow, aseismic slips that occur at depth in the fault beneath the Moho and load the shallower part of fault,’ Nabelek said.
‘We can see a relationship between mantle slip and crust slip. The slip at depth most likely triggers the big earthquakes. The big ones are preceded by foreshocks associated with creep.’
IS CALIFORNIA AT RISK OF A DEVASTATING MEGAQUAKE?
A recent report from the U.S. Geological Survey has warned the risk of ‘the big one’ hitting California has increased dramatically.
Researchers analysed the latest data from the state’s complex system of active geological faults, as well as new methods for translating these data into earthquake likelihoods.
The estimate for the likelihood that California will experience a magnitude 8 or larger earthquake in the next 30 years has increased from about 4.7% to about 7.0%, they say.
‘We are fortunate that seismic activity in California has been relatively low over the past century,’ said Tom Jordan, Director of the Southern California Earthquake Center and a co-author of the study.
Shown above is the chance of an earthquake across California over the next 30 years
‘But we know that tectonic forces are continually tightening the springs of the San Andreas fault system, making big quakes inevitable.’
Seismologist Lucy Jones from the US Geological Survey warned recently that people need to accept the fact catastrophe is imminent, and prepare themselves accordingly.
Dr Jones said our decision to not accept it will only mean more people suffer as scientists warn the ‘Big One’ is now overdue to hit California.
Dr Jones, who is from the US Geological Survey said there are three key reasons why the peril is so frightening – it cannot be seen, it is uncertain and it seems unknowable.
This means people bury their heads in the sand and pretend it won’t happen.
Earth’s different layers differ in their ability to lock and accumulate stress, the team explains.
This phenomenon is known as seismic coupling.
‘The crust is fully coupled – all slip is released in a seismic way,’ Kuna said.
‘Fault in the shallow mantle is partly coupled, partly not, and releases slip both seismically and aseismically.
‘The deep mantle is fully creeping, uncoupled, with no earthquakes. But the fault is loaded by this creep from beneath – it’s all driven from beneath.
‘Our results also show that an aseismic fault slip may trigger earthquakes directly, which may have implications for active faults on land.’