Reverberations felt for miles, caught on cameras in offices along the coast and at an airport.

Please evacuate right now.

Tsunami warnings issued following the quake urging some residents to leave the seaside, but so far, injuries and damage have been minimal. Researchers have long warned of a megaquake eight or nine magnitude, potentially even more damaging than the 9.1 that set off a tsunami in 2011 and ravaged Japan's northeast coast. The disaster, one of the worst in this century, killing more than 18,000 people, leaving parts of the country in ruin, including a nuclear disaster at Fukushima that rattled the world.

There was a magnitude 7.3 earthquake that happened two days before that earthquake, and about five percent of the time, we see that there is an earthquake called foreshock that precedes a larger event.

Japan sits on the circum-Pacific belt known as the Ring of Fire, where tectonic plates meet, leading to lots of quakes and volcanic activity. The U.S.'s Pacific coast also on the Ring of Fire.

Southern California just getting hit with a 5.2 magnitude quake Wednesday.

Experts believe we should be ready for one of those megaquakes too.

There's a lot of effort being put into preparing for such an event in terms of both the seismic hazard, the ground shaking, and the tsunamis.

Preparing for what seems unthinkable, but might be inevitable.

Dana Griffin, NBC News.

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