Is the San Andreas fault line at risk of the 'BIG ONE'? New-found 15 mile-long formation in the area could be ground zero for California's next massive earthquake
- Experts mapped the southern 20 miles of the 15 mile long fault zone to make the new discovery
- They found a highly faulted, never before seen area in the region called the Durmid ladder structure
- It is 0.6 to 2.5 miles wide and is found in the upper 1.8 to 3.1 miles of the ground
- Scientists say there's a 75% chance for a magnitude seven or larger event in California within 30 years
A tectonic time bomb that threatens to set off a huge earthquake under California could be triggered by a newly-discovered structure in the San Andreas fault.
Experts believe a newly-uncovered 15 mile (25km) long formation, dubbed the Durmid ladder structure, could be ground zero for the next major earthquake to hit the region, colloquially known as 'Big One'.
The discovery was made during an extensive geological study which examined the southern tip of the (1,300-km) long fault zone, which many believe will set off the next big earthquake.
A tectonic time bomb that threatens to set off a huge earthquake under California may be triggered by a newly discovered structure in the San Andreas fault. Experts uncovered a 15 mile (25 km) long formation, dubbed the Durmid ladder structure
Researchers say the Durmid ladder structure, located in the square region above, could be ground zero for the next major earthquake to hit the fault, colloquially known as 'Big One'. It is organised in a sheared ladder-like structure found in the upper 1.8 to 3.1 miles of the ground
Researchers have been warning that the state is overdue for a highly destructive earthquake since early last year.
A new study has also found that there's a 75 per cent chance for a magnitude seven or larger event in both northern and southern California within the next 30 years.
That's thanks to 'slow earthquakes' that pass unnoticed by people, but which experts say can trigger large destructive quakes in their surroundings.
Scientists from the Geological Society of America found the structure using detailed geologic and structural mapping of the southern 20 miles (30 km) of the San Andreas fault zone in southern California.
It was named the Durmid ladder structure because it is located in the Durmid Hill region, a highly-faulted area of rock that is 0.6 to 2.5 miles (one to four km) wide.
The Durmid ladder structure is found in the upper 1.8 to 3.1 miles (three to five km) of the ground and, as its name suggests, has a broken ladder-like pattern.
Fears of California's 'Big One' were stirred in May 2017, when an expert warned that a destructive earthquake will hit the state 'imminently'. Pictured is a view of the San Andreas fault in the Carrizo Plain
The structure extends from the well-known main line of the San Andreas fault on the northeast side, to a newly identified East Shoreline fault zone on the opposite edge.
Experts say that if seismic activity triggered the collapse of the Durmid ladder structure and the wider San Andreas Fault, the effects would likely be felt across a 15 square mile (40 sq km) area.
The exact effects are hard to predict, due to the unusual shape of the ladder, with fault lines extending both vertically and horizontally.
The strength of the earthquake would depend on whether the whole structure collapsed at once, or if each of the fault lines was triggered individually.
However, at its worse, the Durmid latter could result in a devastating magnitude 7.5 or stronger earthquake, researchers have forecast.
Writing in a paper on the findings, its authors said: 'The great width of the East Shoreline fault zone in Durmid Hill and the even larger width and spatial extent of the Durmid ladder structure imply that surface faulting hazards from a major earthquake rupture in this part of the San Andreas fault zone might be dispersed across a 15 square mile (40 sq km) area, if both master faults and the intervening cross faults are activated at once.
'If ladder-like strike-slip fault zone rupture in a piecemeal fashion they will have an especially unpredictable surface-faulting hazard.'
San Andreas Fault in the Carrizo Plain, aerial view from 8500 feet altitude. Experts say that if seismic activity triggered the collapse of the Durmid ladder structure and the wider San Andreas Fault, the effects would likely be felt across a 15 square mile (40 sq km) area.
Fears of California's 'Big One' were stirred in May 2017, when an expert warned that a destructive earthquake will hit the state 'imminently'.
Seismologist Dr Lucy Jones, from the US Geological Survey, warned in a dramatic speech that people need to protect themselves, rather than ignore the threat.
Researchers have been warning since early last year that the state is overdue for a highly destructive earthquake. Pictured is the destruction after the magnitude 6.7 Northridge earthquake hit Los Angeles in 1994
Dr Jones said people's decision not to accept it will only mean more suffer as scientists warn the 'Big One' is now overdue to hit California.
In a keynote speech to a meeting of the Japan Geoscience Union and American Geophysical Union, Dr Jones warned the public is yet to accept the randomness of future earthquakes.
WHAT ARE THE 'SLOW EARTHQUAKES' DETECTED IN THE SAN ANDREAS FAULT?
Synthetic aperture radar data for 2003 to 2010 let researchers team map the average rate of movement for the central section of the San Andreas Fault (black line). Red shows ground movement toward the southeast, and blue to the northwest
Geologists have long thought that the central section of California's famed San Andreas Fault - from San Juan Bautista southward to Parkfield, a distance of about 90 miles (145 km) - has a steady creeping movement that provides a safe release of energy.
Creep on the central San Andreas during the past several decades, so the thinking goes, has reduced the chance of a big quake that would rupture the entire fault from north to south.
New research, however, shows that the earth movements along this central section have not been smooth and steady, as previously thought.
Research by two Arizona State University geophysicists found the activity has been a sequence of small stick-and-slip movements - sometimes called 'slow earthquakes' - that release energy over a period of months.
Although these slow earthquakes pass unnoticed by people, experts say they can trigger large destructive quakes in their surroundings.
One such quake was the magnitude six event that shook Parkfield in 2004.
'What looked like steady, continuous creep was actually made of episodes of acceleration and deceleration along the fault,' said Mostafa Khoshmanesh, a graduate research assistant in ASU's School of Earth and Space Exploration (SESE)
'Based on current time-independent models, there's a 75 per cent chance for an earthquake of magnitude seven or larger in both northern and southern California within next 30 years.'
He is the lead author of a Nature Geoscience paper reporting on the research.
'We found that movement on the fault began every one to two years and lasted for several months before stopping,' said Manoochehr Shirzaei, assistant professor in SESE and co-author of the paper.
The central San Andreas Fault (green) is flanked by sections (red) that are far more active. New research, however, shows that the earth movements along this central section have not been smooth and steady, as previously thought
'These episodic slow earthquakes lead to increased stress on the locked segments of the fault to the north and south of the central section,' Shirzaei said.
He points out that these flanking sections experienced two magnitude 7.9 earthquakes, in 1857 in Fort Tejon and 1906 in San Francisco.
The scientists also suggest a mechanism that might cause the stop-and-go movements.
'Fault rocks contain a fluid phase that's trapped in gaps between particles, called pore spaces,' Dr Khoshmanesh said.
From 2003 to 2010 (bottom scale), portions of the fault at different distances from Parkfield (left scale) moved at varying rates. Red shows periods when the movement was greater than average, blue when it was less
'Periodic compacting of fault materials causes a brief rise in fluid pressure, which unclamps the fault and eases the movement.'
The two scientists used synthetic aperture radar data from orbit for the years 2003 to 2010.
This data let them map month-to-month changes in the ground along the central part of the San Andreas fault.
They combined the detailed ground-movement observations with seismic records into a mathematical model.
The model let them explore the driving mechanism of slow earthquakes and their link to big nearby quakes.
'We found that this part of the fault has an average movement of about three centimeters a year, a little more than an inch,' Dr Khoshmanesh said.
'But at times the movement stops entirely, and at other times it has moved as much as 10 centimetres a year, or about four inches.'
The picture of the central San Andreas Fault emerging from their work suggests that its stick-and-slip motion resembles on a small timescale how the other parts of the San Andreas Fault move.
They note that the new observation is significant because it uncovers a new type of fault motion and earthquake-triggering mechanism, which is not accounted for in current models of earthquake hazards used for California.
Dr Shirzaei said: 'Based on our observations, we believe that seismic hazard in California is something that varies over time and is probably higher than what people have thought up to now.'
He added that accurate estimates of this varying hazard are essential to include in operational earthquake-forecasting systems. 
The area highlighted in red on this map indicates the region covered by the Geological Society of America's original chart above
People should be preparing now, she warned.
Dr Jones and her team have published a scenario of a 7.8 earthquake on the San Andreas fault, which they predict could kill many people and devastate 15,000 buildings.
In 2011, a magnitude nine earthquake hit the east coast of Japan and killed some 20,000 people.
'The city leaders ignored protocol that said to move to higher ground and conducted their emergency meeting in the city hall', said Dr Jones.
'When the tsunami poured over the sea wall, they lost over 1,000 people, including most of their city government'.
The full findings of the latest study were published in the journal Lithosphere.
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.
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