"It's unusual to have big waves like that coming in. We don't see that everyday," said Kate Hutton of the U.S. Geological Survey.
Caltech scientists monitor seismic activity and say Haiti is in a very active area of the world.
In fact the Caribbean islands were originally created by earthquakes. Eight quakes of 7.0 magnitude or greater have struck the area in the past 220 years.
Haiti is surrounded by two major plates that are pushing on a fault line that runs from Jamaica through southern Haiti. On Tuesday, that fault finally broke causing the two plates to slip past each other along an approximately 40-mile stretch of the earth.
The ground shook so violently because the rupture was so close to the surface - within just eight miles.
The seismic energy of the 7.0 magnitude earthquake is the same as 32,000 small atomic bombs.
Scientists believe the quake was so large because pressure has been building up in this fault ever since the last major earthquake hit here - 240 years ago. Scientists warned the island was primed for another mega-quake. In fact, in 2008, five scientists issued a paper predicting a 7.2 magnitude quake along the fault. They say the risk of another large quake still exists.
"By releasing strain on one part of the fault, you actually increase strain on adjacent parts of the fault thereby making them more susceptible to a large earthquake," said Dr. Paul Mann of the University of Texas Institute for Geophysics.
The fault under Haiti is the same type as the San Andreas fault - the 800-mile long scar slicing through California. Pressure has been building in the southern end near Los Angeles for more than 300 years. Scientists say the so-called "big one" here is not a matter of if - but when.
At the Caltech lab, a simulation shows a major earthquake near Los Angeles. Scientists here believe there is a 99.7 percent chance of a 6.7 or larger earthquake here in California in the next 30 years.