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An underwater fault line along the US west coast could trigger a mega-earthquake that would be more devastating than California’s “Big One,” a new study suggests.

Using underwater mapping techniques, scientists have mapped the Cascadia subduction zone—a 600-mile fault line stretching from southern Canada to northern California—in unprecedented detail.

The fault was revealed to be splitting into four segments instead of being one continuous strip like most fault lines. The discovery could prove more catastrophic because tectonic plates can slide under each other, creating more pressure and stronger earthquakes.

The researchers concluded that the Cascadia subduction zone has the potential to trigger a magnitude nine plus earthquake.

By comparison, San Andreas in California is ready for an earthquake of up to 8.3 on the Richter scale.

If an earthquake greater than magnitude 9 struck the US West Coast, it could generate a tsunami reaching 100 feet or more, kill more than 10,000 people and cause more than $80 billion in damage in Oregon and Washington alone.

Disaster contingency plans in Oregon and Washington warn that after such a strong earthquake, they could face a wave of lingering deaths from diseases from exposure to dead bodies, animal carcasses, contaminated water and hazardous spills from commercial, industrial and domestic sources.

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A similar fault zone off the coast of Japan erupted in 2011, creating a magnitude 9 earthquake that triggered a devastating tsunami to hit the country, killing nearly 20,000 people.

Scientists now worry that a similar disaster could hit the US in the coming years, reporting that earthquakes caused by Cascadia occur roughly every 500 years, with the last occurring in the 1700s.

“The recurrence interval for this subduction zone for major events is on the order of 500 years,” Wang said.

“It’s hard to know exactly when it’s going to happen, but certainly if you compare this to other subduction zones, it’s pretty late.”

Cascadia’s four segments make it more dangerous than other major fault lines because they have different rocks and sediments, with the most worrisome stretch stretching along northern Oregon, into Washington and southern British Columbia.

“This requires a lot more study, but for places like Tacoma and Seattle, it could mean the difference between alarming and catastrophic,” said study co-author Harold Tobin, a geophysicist at the University of Washington.

This section of Cascadia is flatter and smoother than the other three sections, meaning it can cause the largest earthquakes that extend further inland into the US and affect all of Washington’s coastal communities.

“We have the potential for earthquakes and tsunamis as large as the largest we’ve experienced on the planet,” Tobin told NBC News.

“Cascadia appears capable of generating magnitude nine or slightly less or slightly greater.”

Suzanne Carbotte, lead author of the study and a marine geophysicist at the Lamont-Doherty Earth Observatory, said this is the first clear picture of the Cascadia area, adding that all emergency response models are based on “old, low-quality data from the 1980s- those years”.

The researchers hope their findings will help states in the impact zone prepare for a worst-case emergency response and evacuation scenario if the Cascadia subduction zone ruptures.

Neither Oregon nor Washington state is sufficiently prepared for this type of disaster because of the limited information in the Cascadia model from the 1980s, according to the researchers.

However, they said new readiness assessments could be released as early as next year.

The subduction zone map was created using an active seismic imaging source – which beams sounds down to the ocean floor and processes the echoes – which gives a clearer picture of how it may be affecting the environment.

Researchers at the Columbia Climate School attached a streamer — a nine-mile cable — to the back of the boat, which used 1,200 hydrophones that picked up the echoes to update their ocean acoustic tomography models that provide images of the fault.

The hydrophones measure the time it takes for sound to bounce off structures on the ocean floor and reach the surface, allowing them to detect differences in rock elevation that signify recently active fault lines.

“The accuracy and this resolution is truly unprecedented. And it’s an amazing set of data,” Kellyn Wang, a researcher with the Geological Survey of Canada who was not involved in the study, told NBC News.

“It just allows us to do a better job of assessing risk and having information about building codes and zoning.”