Whether a huge earthquake will hit California could come down to this one thing

With so much going on in the world, we wouldn’t blame you for feeling a bit stressed.

Things are so stressful, apparently, that even the faults that slice through California are under record-breaking stress, a study has found.

The Los Angeles region sits in the tension-wracked meeting point of the North American and Pacific tectonic plates, making earthquakes common.

New models found that tectonic stress in the region is higher today than at any point over the last millennium, suggesting a ‘Big One’ is overdue.

But when this massive quake could happen all depends on a single location: a busy highway intersection not far from LA.

California primed for a ‘large future rupture’

According to a paper published in the Journal of Geophysical Research, 36 quakes of magnitude 6.4 or larger have occurred in the Los Angeles region in the last 1,000 years.

The last major earthquake that shook LA was the Fort Tejon quake of 1857, with a magnitude of 7.9. 

Tectonic stress has been building up ever since, an unnerving ‘quiet period’ that hints at a ‘large future rupture’, lead author Dr Liliane Burkhard of the University of Bern in Germany said.

Tectonic plates sit on spongy magma and are always moving around. When they pull in opposite directions, they sometimes get stuck.

Yet these slabs of Earth still try their best to move, creating a lot of push-and-pull tension that has nowhere to go.

Eventually, this reaches a breaking point and releases huge amounts of pent-up energy, which shakes the Earth’s surface – an earthquake.

While this sounds like a simple, step-by-step process, earthquakes are nearly impossible to predict and can happen at a moment’s notice.

Burkhard, together with experts from the University of Hawai’i at Mānoa, tried to see if there were any patterns in how quakes happen in LA to help better understand the conditions that come before massive ones.

The region is the meeting place of two grinding fault systems that stretch hundreds of miles, the San Andreas and San Jacinto faults.

Each together accommodates about 90% of the motion between the Pacific and North American plates.

But what piqued Burkhard’s interest is where the fault systems approach one another: Cajon Pass.

The point is between the San Bernardino Mountains and the San Gabriel Mountains, only 40 miles or so from the city of Los Angeles.

By modelling a millennium’s worth of quakes and shakes, Burkhard found Cajon Pass is an ‘earthquake gate’, where a rupture on one fault can ripple onto the other.

The 1857 earthquake, for example, only impacted a single fault as the gate was ‘shut’. Yet another event in 1812 rumbled across both fault systems.

Whether this intersection is open or closed, in other words, plays a big role in deciding how far-reaching the ‘Big One’ would be.

Burkhard said that current stress levels suggest the next earthquake will shake both faults.

‘The earthquake gate concept captures something important about how fault junctions work,’ she said.

‘Cajon Pass doesn’t simply block or channel earthquakes: It responds to stress conditions, and those conditions change over centuries.’

Quakes occurring in southern San Andreas are a big concern, given that Los Angeles County is home to nearly 10 million people.

The roads, railway tracks and energy lines lacing Cajon Pass feed into the Los Angeles area, San Bernardino, Riverside, and the Coachella Valley.

Burkhard said: ;So not only is it concerning that the stresses are reaching historic highs but also that the relative stress conditions between the two fault systems are approaching the range we associate with major ruptures crossing both faults simultaneously – and that is a scenario with much larger consequences for the region.;

She stressed that her findings aren’t a prediction of when a quake will happen.

‘What we can say is that the system is critically stressed and that physics-based models like ours give a clearer picture of the range of scenarios we should be prepared for,’ Burkhard added.

‘This information is important for hazard assessment, infrastructure planning and emergency preparedness.’

There is a 31% chance that an earthquake measuring magnitude 7.5 or higher will upend the Los Angeles area in the next 30 years, according to the US Geological Survey.

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