Fears of the ‘Big One’ – an earthquake so big it devastates all of California – have risen to new heights after a disturbing discovery under America’s most dangerous fault line.
Researchers from the US and Switzerland revealed that the San Andreas Fault has reached its highest levels of stress in 1,000 years – adding that it has been more than 160 years since the giant crack in the Earth’s crust had a major release of energy.
The San Andreas is an 800-mile-long fault line which runs under most of California, passing by Los Angeles in the south and San Francisco in the north and connecting to several other major faults, most notably the San Jacinto Fault near Los Angeles.
This connection is where researcher Liliane Burkhard from the University of Hawaiʻi at Mānoa said seismic stress has become so great at the southern end of the San Andreas that a rupture could travel along both fault lines – resulting in a mega quake.
Burkhard said: ‘Right now, with stress at historically high levels across the region and more than 160 years elapsed since the last major rupture, the system is in a critically loaded state.’
The study did not predict that the ‘Big One’ was imminent but did warn that such a seismic event would likely impact ‘densely populated areas including Los Angeles, San Bernardino, Riverside and the Coachella Valley.’
Previous studies of the San Andreas and other faults in California have concluded that there is a 99 percent chance of a major quake stronger than magnitude 6.7 within the next two decades.
Experts with the US Geological Survey have predicted that a massive earthquake striking under Los Angeles would cause hundreds of deaths, tens of thousands of injuries and $200 billion in damages.
Experts fear that the San Andreas Fault close to Los Angeles is primed for the major eruption as stress levels have reached a 1,000-year peak (Stock Image)
Researchers in Hawaii found the stress is also at historic levels along the connecting San Jacinto Fault
The research team discovered that stress, also known as built-up pressure underground, on the southern San Andreas Fault was now higher than at any time in centuries at a specific point called the Mojave South section near Cajon Pass.
This stress is best described as energy slowly squeezing the locked fault. The two sides of the fault, the Pacific Plate and the North American Plate, are trying to slip past each other but are often stuck together.
The more stress builds up, the more likely the locked section will suddenly break free and slip past each other, releasing energy as an earthquake.
Scientists measured this pressure in units called MPa, or megapascals. MPa is a standard unit used by engineers and scientists to describe stress and pressure inside rocks and materials. One MPa equals one million pascals, the basic scientific unit of pressure.
Right now, this key section of the San Andreas Fault has 2.8 MPa of stress, which is at or above the level where it has usually broken during major earthquakes over the last millennium.
The nearby San Jacinto Fault was found to be even higher at 3.6 MPa – the highest pressure recorded on that fault in the entire 1,000-year history of the study.
The two faults meet at Cajon Pass, which the study authors compared to a ‘gate’ that can either stop a quake or let it pass through to both faults.
Burkhard warned that when both faults carry this much high stress at the same time, a future earthquake starting on one of these faults could more easily go through the gate and jump to the other fault, creating one much larger disaster instead of two smaller ones.
The San Andreas and San Jacinto Faults connect at the Cajon Pass, which can stop an earthquake from traveling farther or allow the quake to become a bigger disaster
Pictured: The San Andreas Fault in California
‘This is not a prediction of when an earthquake will happen,’ Burkhard said in a statement.
‘What we can say is that the system is critically stressed, and that physics-based models like this one give us a clearer picture of the range of scenarios we should be prepared for.’
The study published in the Journal of Geophysical Research: Solid Earth created a detailed computer model that acted like a video game simulation of earthquakes along the San Andreas.
Researchers fed their model real historical data from the last 1,000 years, including carbon dating of rocks and old tree rings that provided a living record of past quakes.
The model simulated how the Earth’s plates slowly push against each other, building up pressure over time and then suddenly releasing that pressure in the form of a disastrous seismic event.
The most recent predictions from USGS have looked at a magnitude 7.8 earthquake along the San Andreas Fault originating right in Los Angeles, a city of 3.8 million people.
This hypothetical ‘Big One’ would cause roughly 1,800 deaths, 50,000 injuries, and $200 billion in damages, according to the Great California ShakeOut.
USGS carried out a simulation of a massive 7.8 magnitude earthquake in Southern California in 2008. The predictions included hundreds dying and up to $200 billion in damages
Los Angeles has seen some of the largest quakes in California, including the 1994 Northridge earthquake, one of the most destructive and deadly in the state’s history.
This magnitude 6.7 event toppled buildings across Los Angeles, Ventura, Orange and San Bernardino counties. The quake killed 60 people, injured more than 7,000 and left thousands more homeless.
A major rupture along any segment of the southern San Andreas Fault has not occurred since the great Fort Tejon earthquake of January 9, 1857.
