All of America’s deadly ‘time bomb’ earthquake zones revealed… and when the ‘Big One’ could strike

Americans have long lived in fear of the ‘Big One’ – an earthquake so enormous it would devastate the West Coast.

The harrowing images of Thailand and Myanmar on Friday morning after a 7.7 magnitude earthquake struck the region lay bare only too clearly the horrifying reality of the damage a quake this size can cause. 

Thousands are feared dead, buildings have been destroyed and there are concerns of catastrophic flooding from a possible dam collapse.

In America, growing fears of a deadly disaster are no longer confined to the Golden State. As earthquakes hit across the country, many citizens are terrified that they too could be sitting on a seismic ‘time bomb’. 

Geologist Robert Yeats, author of ‘Earthquake Time Bombs’, has highlighted the risks associated with the presence of several large US cities in the Pacific Northwest’s Cascadia subduction zone.

‘Groups of experts have prepared resilience surveys in the states of Washington and Oregon to determine the consequences of not getting ready for the earthquake disaster ahead of time,’ Yeats wrote.

Even parts of New England and Texas have been struck by record-setting earthquakes in the last year after more than a decade of relative quiet.

But America’s West Coast is still where geologists are watching most carefully and there is reason to believe a seismic cataclysm could happen soon.

The US Geological Service (USGS) said there have already been several ‘significant’ earthquakes in California this year. And in 2024 the state was rattled by more quakes than at any point in the past three decades. 

Experts also warned that some areas are woefully unprepared for these so-called ‘time bomb’ earthquakes, which they say could cause thousands of deaths and billions in damages.

Predicting the exact moment an earthquake will strike is impossible, so scientists instead use historical activity to try to understand the patterns of seismic events.

Steven Sobieszczyk, a spokesperson for USGS, explained that scientists have combined historical records with current seismic readings to work out where the highest risks are today. 

The Cascadia Subduction Zone

An area in the Pacific Northwest lies on a ‘subduction’ zone where a tectonic plate slides underneath the North American plate.

Subduction zones produce the world’s largest earthquakes. 

These quakes occur when friction between the two plates causes them to become locked, and stress begins to build along the border between them, also known as a fault. 

Eventually, the stress exceeds the strength of the fault and it breaks free. This causes a shockwave of stored energy to travel up towards Earth’s surface, which we feel as an earthquake. 

The Cascadia subduction zone stretches from northern California all the way to Canada’s British Columbia. It also sits under Oregon and Washington and extends off shore into the Pacific Ocean.

Experts say the area has ‘extraordinarily’ low rates of earthquakes in recent times, but that in itself could mean that stress is building.

Researchers believe that around eight big earthquakes have shaken this area in the past 3,500 years and another could be ‘due’ to hit the region in the near future.

‘This tectonic boundary experienced a great earthquake [magnitude 9] in the year 1700,’ Sobieszczyk said.

‘Intense earthquake shaking was recorded by civilizations residing in the area during 1700 and caused large tsunami waves that propagated across the ocean,’ the USGS expert added.

Predictions of what might happen if a similar quake struck the Cascadia subduction zone today have suggested it could be the worst natural disaster in the history of North America.

Experts warn that the Cascadia subduction zone could unleash ‘The Big One’ – an extremely powerful earthquake that may devastate the West Coast

The US West Coast is an earthquake hotbed, and USGS projections warn that the worst zones line the entire coast from California to Washington. The red area near Memphis shows the New Madrid seismic zone, which is also highly active

Projections warn that thousands of landslides could strike, with 7,000 road bridges collapsing.

FEMA, the natural disaster agency, calculates that 85 percent of ports and drinking water plants would be seriously damaged or destroyed, as well as 77 percent of the region’s airports, railways, schools, and hospitals.  

Evidence left by the previous Cascadia earthquake offers further insight into the devastation the subduction zone could unleash.

Radiocarbon dating shows forests were submerged in salt water as the land suddenly subsided 300 years ago during the last major quake.

Using calculations for the speed of a trans-Pacific tsunami wave, researchers estimate that the quake took place on January 26, 1700, at around 9pm PT.

Yeats added that the ‘repeat time’ — or the time between major earthquakes – varies from 1,200 years in the northern part of the Cascadia zone to just 250 years in the southern part closest to California.

This is what has led many experts to believe Cascadia is ‘overdue’ for a major seismic catastrophe.

‘This means that scientists can say that without a doubt, there will be more great earthquakes at Cascadia, but they can’t say when the next one will strike — tomorrow or a century from now,’ Yeats explained.

Could a massive earthquake unleash a devastating tsunami on the US? Earthquakes trigger tsunamis by causing the ocean floor to rise or fall, pushing water above to form a huge wave

The Cascadia zone, which sits under Washington, Oregon, and northern California, is said to be ‘overdue’ for another major earthquake

If ‘The Big One’ does strike soon, Yeats predicted that gas escaping from underground lines would catch fire.

The earthquake would also be followed by a tsunami similar to the 2011 Tohoku-oki tsunami that caused over 18,000 deaths in Japan.

In Oregon alone, property losses would total $32 billion. Towns including Tillamook, Astoria, Seaside, Cannon Beach, Coos Bay, and Newport would all be submerged, with the coast subsiding up to 10 feet permanently.

San Francisco and Northern California

USGS estimates that there is a nearly three-in-four chance of an earthquake striking the San Francisco area in the near future.

Across the whole Northern California region, that risk jumps to 95 percent.

Sobieszczyk explained that the Bay Area has been the focus of many large and destructive earthquakes, including the 1906 San Francisco quake that registered at least 7.7 on the Richter magnitude scale. 

This struck the California coast on April 18, 1906, causing blazes to erupt for days. By the end, 80 percent of the city was destroyed and more than 3,000 people were dead.

Over 300,000 people were also left homeless as 30 fires destroyed 25,000 buildings on 490 city blocks. Rebuilding San Francisco cost $350 million — the equivalent of $8 billion in today’s money.

The three Bay Area faults most likely to cause a huge earthquake are the Hayward fault, the Calaveras fault, and the infamous San Andreas fault — which runs along most of the Californian coast.

Survivors view the wreckage of the Grand and Palace Hotel after the 1906 earthquake in San Francisco, California

Cracks appear in East Street after the earthquake, which was calculated to be anywhere from 7.7 to 8.3 on the Richter magnitude scale

Could an earthquake rock Los Angeles? The major US metropolis is one of several California cities which sits along the San Andreas fault line

Los Angeles

Caltech experts suggest that Southern California is at particularly high risk of a major earthquake.  

Today, Southern California experiences an average of one earthquake every three minutes. 

A study found that between 2008 and 2017, 1.81 million earthquakes (most of them too weak to be felt by humans) struck southern California. 

In 2024, Los Angeles had 2,420 quakes of magnitudes up to 4.6. 

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 Bernadino counties. The quake killed 60 people, injured more than 7,000 and left thousands more homeless. 

According to Sobieszczyk, Southern California is prone to big earthquakes because of a tectonic plate boundary that runs up and down the state’s coastline.

Known as the San Andreas Fault, this boundary marks where the Pacific plate slides past the North American plate, causing great seismic waves. 

The southern section of the San Andreas Fault passes just 35 miles from Los Angeles, so quakes emanating from this fault are likely to strike the city. A big one could cause as many as 1,800 deaths along with damage up to $213 billion.