Minute by minute, what would occur if ‘The Big One’ hit California

An unprecedented level of earthquake activity has rocked California in recent weeks, reigniting fears about the impending ‘Big One.’

The West Coast is overdue for a massive quake along the San Andreas fault, a major fracture in the Earth’s crust that spans 800 miles up and down California.

This anticipated magnitude 8 quake would wreak havoc upon the state’s famous cities, causing roughly 1,800 deaths, 50,000 injuries and $200 billion in damage, according to the California Earthquake Authority.

And experts say this is an underestimate. 

It’s impossible to predict exactly when The Big One – or any earthquake – will occur. 

But experts are ‘fairly confident that there could be a pretty large earthquake at some point in the next 30 years,’ Angie Lux, project scientist for Earthquake Early Warning at the Berkeley Seismology Lab, told DailyMail.com.

Lux has walked DailyMail.com through what will happen when the massive quake hits, from the panic of the first few seconds to the destruction that will ensue.  

The reason experts like Lux are confident the fault line is due a big quake is partly because geologic studies suggest a large magnitude quake occurs along this fault every 150 years (and the last one was 167 years ago). 

So far this year, California has had 14 quakes stronger than magnitude 4. 

The average number of magnitude 4 and above earthquakes for this region is about eight per year.

The heightened activity, while not necessarily a sign of impending doom, has brought fears of The Big One to the forefront again.

The San Andreas fault is the boundary-line between two tectonic plates: the North American and the Pacific. 

Tectonic plates are large, solid pieces of the Earth’s crust that move independently of each other. 

Both the southern and northern sections of the San Andreas fault are locked, which means friction has caused the North American and Pacific plates to stick together along these portions of their boundary.

When part of a fault is locked in this way, stress can build up over time and eventually overcome the friction. 

When all that stored energy suddenly releases, shockwaves travel up through the Earth’s crust and cause an earthquake.

Both the southern and northern sections of the San Andreas fault have roughly equal likelihood of generating a high magnitude earthquake in the next few decades.

But a rupture in the southern section of the San Andreas would be particularly dangerous to Californians because it would go right past Los Angeles. 

First 10 seconds: The dreaded cellphone alert

If the southern San Andreas ruptured near the Salton Sea and triggered a magnitude 8 earthquake, an early earthquake warning would be dispatched almost immediately.

‘As soon as that earthquake starts, in the first few seconds of it starting, our sensors are detecting it, and we’ve now created an alert even before the rupture has finished,’ Lux said. 

Those alerts will be sent to anyone in the path of the rupture as it moves up and down the fault line, appearing as a notification on their phones.

At first, the shaking will be relatively weak – the violent shaking will come later.

‘That’s not to say that you can’t have really strong shaking right off the bat. But typically what we see is that the strongest shaking happens a few tens of seconds  into the shaking,’ Lux said. 

That’s because the seismic waves that are released in the first seconds after a rupture are ‘P waves.’ 

These travel very fast, about 3.7 miles per second. But they generate less ground movement than ‘S waves,’ which take longer to occur.

According to a video simulation by The Great California Shakeout, a magnitude 7.8 quake near the Salton Sea would generate shaking up to intensity level five near the epicenter in the first 10 seconds. 

This level of shaking would be felt by everyone in the area but would only cause slight damage, according to the USGS. 

Further out from the epicenter, small towns within 20 miles of the Salton Sea – including Mecca, Salton City and Calipatria – could feel shaking up to intensity level four. 

This level of movement is considered ‘light’ and would mostly be felt by people indoors. It would feel ‘like a heavy truck striking a building’ and would make parked cars rock side to side, according to the USGS.

30 seconds: Buildings come crashing down

At the 30 second mark, cities and towns within a 60 mile radius of the epicenter that are located directly on the fault line – such as Palm Springs – could have shaking up to intensity level 9. 

‘You’re going to see a lot of high-intensity ground shaking at that point,’ Lux said. 

This level of ground movement is considered ‘violent,’ and could cause significant damage to buildings – even causing some to collapse or shift off their foundations, according to the USGS. 

That’s because by then, the rupture would be producing S waves, which travel slower but cause far more damage than P waves, Lux said. 

S waves travel about 2.5 miles per second, but generate high-intensity, side-to-side ground shaking that can topple buildings and knock you off your feet.

Locations further away from the fault line but still within 60 miles of the epicenter – such as Four Corners and Blythe – could see intensity level six to seven shaking. This is considered ‘strong’ or ‘very strong’ ground movement. 

But the amount of damage to areas affected by this level of shaking will depend on how buildings are built, Lux said. 

Some areas could see considerable damage to poorly built or designed buildings and some broken chimneys, according to the USGS. 

‘Here in the US, we would not expect to see buildings falling down, collapsing left and right,’ Lux said. ‘In California, we have building standards.’

These standards mean that most buildings are designed to withstand high-magnitude earthquakes, but even well-built structures could see some slight damage, according to the USGS. 

It’s plausible that people could be injured by this level of shaking, especially due to the risk of falling objects dislodged by the ground movement, Lux said. 

‘At that point, you’re going to have furniture falling, you might have some plaster falling from the ceiling, or light fixtures or whatnot,’ she said. 

Though many people may attempt to run out of their building during a high-magnitude earthquake, this is highly unsafe. 

‘That’s why our advice to people when they get a warning or when they feel shaking  is to drop, cover and hold on,’ she added. ‘Once that strong shaking hits, you can’t move.’

Also by this time, lower intensity shaking – between level three and four – would have expanded significantly, affecting cities such as San Diego and San Bernadino. 

One minute: LA bears the brunt

According to the Shakeout scenario, intensity level two to three shaking would reach LA about 45 seconds after the initial rupture near the Salton Sea. 

By 75 seconds, high-intensity shakes would be rolling in, steadily increasing ground movement until the most violent shaking – up to intensity level nine – hits at about 90 seconds.

Violent shaking could rock LA for at least a minute, according to the Shakeout scenario. 

In that time, extensive damage will likely have occurred – crumbling buildings and causing them to shift off their foundations. As infrastructure is destroyed, many residents will likely be injured or perhaps even killed. 

And because of the geology beneath LA, shaking could be amplified even more, Lux said.

‘The issue with LA particularly is there’s the LA basin,’ she explained. ‘It’s got mountains around the outside and a lot of really soft sediment in the basin.’

The city is built right on top of this soft sediment. ‘You can think of that basin area – basically everything that LA is sitting on – as a big bowl of Jell-O,’ Lux said.

‘As the waves come in, they’re going to get trapped in that basin and amplified. So there could be significant damage because of that amplification,’ she added.

Two minutes and beyond: aftershocks

The mainshock will most likely subside by two minutes after the initial rupture, Lux said. But people will not have long to recover, as aftershocks will quickly set in.  

For example, when the magnitude 7.1 Ridgecrest earthquake rocked California in 2019, systems ‘had a hard time detecting earthquakes for 15 minutes afterwards because there was so much noise – so many aftershocks happening,’ Lux said.

Aftershocks happen near the fault zone where the mainshock rupture occurred and are part of the ‘readjustment process’ after the main slip on the fault, according to the USGS. 

They are usually lower in magnitude than the mainshock, but can still cause significant damage, injuries and even deaths. 

‘If you have a magnitude 8 earthquake, or magnitude 7.5 earthquake, you could see aftershocks up to magnitude 6.5,’ Lux said. But it’s impossible to predict exactly how severe aftershocks will be. 

Both the number and magnitude of aftershocks will gradually decrease over time. But technically, aftershocks can persist for days, weeks, or even years after the main shock occurs, Lux said. 

A few weeks after the mainshock subsides, however, experts typically stop referring to these smaller quakes as aftershocks, she added. 

When The Big One is all said and done, California could be left with hundreds of billions of dollars in damages and thousands of people injured or killed. 

‘From an infrastructure point of view, we’ve done our best to prepare. We build our buildings to code, we have emergency plans in place,’ Lux said. 

But many Californians are not prepared for a high-magnitude earthquake. 

‘If you were to go around and ask how many people have an earthquake preparedness kit? How many people have a two week supply of water? How many people have food and medications for two weeks? You may not find many people responding affirmatively, unfortunately,’ Lux said. 

Californians should always remember that they live in earthquake country, she added. The San Andreas could rupture at any time, and people will need to be ready if they want to survive.