The Big One. Those three words make locals along the West Coast of North America shudder with fear. This area is plagued by earthquakes. But hey, at least they are ready. Unlike the middle of the continent, which is woefully unprepared for the event that physically rips the United States in half.

What could cause this? What would the destruction look like? Would the U.S. become two separate countries?

Megathrust earthquakes are the largest and deadliest seismic events on Earth. They occur along fault lines, where the edge of one plate is forced downward into the hot mantle beneath another plate.

The Cascadia subduction zone along the West Coast of North America last caused a megathrust earthquake on January 26, in the year 1700. And many people claim that it’s overdue for another one.

The Cascadia subduction zone is created by the Juan de Fuca oceanic plate which is moving down into the mantle of the North American plate. It’s not a smooth movement though, and pressure builds as the plates lock together. And builds. And builds.

Until the North American plate suddenly pops on top of the older Juan de Fuca plate. This would trigger a megathrust earthquake, decimating the Western coastline of the United States. But that’s not all.

Somehow, the force of this terrifying earthquake causes the thinnest part of the tectonic plate, between California and Colorado, to snap. This is now an end of days nightmare scenario. A crack races from California all across the United States, splitting the nation in two.

This deafening event would cause roads to crumble, houses to fall into the giant crevice, and many deaths. Water from the Pacific and Atlantic oceans would rush in to fill the void, causing 3 meter high(10 feet) tsunamis and flooding along the midline of the U.S.

Roads, power lines, and sewer pipes would tear apart. Pipelines carrying crude oil would burst, adding toxic oil to the massive floods. It would take a national effort to clean up and rebuild both the coastline and Middle America. Hopefully, it would bring the country together.

And after all the rubble is cleared, we would begin to assess our new, physically split nation. The rift would only be about 20 m (65 ft) wide. You’d be able to wave to your neighbors from across the divide.

The two sides would gradually drift apart, at about 3 to 5 centimeters (1 – 2 inches) per year. And the rift would eventually grow and form a new ocean, but for now it’s just a canal. At first, you would rely on ferries to shuttle people, cars, and supplies between the two halves.

Although, it wouldn’t be the smoothest sailing. Because the Atlantic and Pacific oceans have different temperatures and levels of salt, the mixing of the two could create rough water.

Eventually, we would engineer segmented bridges that could be elongated as the rift grows. The canal itself would be used as a quicker shipping route between the West Coast and Europe.

Middle America would develop shipping ports, waterfronts, and beaches, which would attract tourists and new residents. The new middle coastline would explode in population, with large cities growing along this new transportation route. The U.S. would likely stay a single nation for a while. It just went through a shared, tragic event, and the rift is only 20 m (65 ft) wide, after all.

But as the newly separated plates began to move farther away, differences in culture and politics could increase. And the possibilities of the two sides politically splitting up would look more inevitable.

After many years of division, there could be a South United States and North United States. The probability of the United States physically breaking in two is very low to impossible.

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