THE earthquake that hit Haiti had 35 times the force of the Hiroshima atomic bomb – and resulted from a combination of deadly factors.
Haiti sits on the boundary of two tectonic plates – the Caribbean and the North American – creating a fault system across the country.
Known as the Enriquillo-Plantain Garden fault, this sees the two plates moving past each other.
Yesterday's quake had a magnitude of 7.0 on the Richter scale – almost as powerful as the country's worst recorded, in 1751 with a magnitude of 7.3.
But seismologists said that what made yesterday's quake even more deadly was that it was "shallow" – close to the surface and so causing greater shaking of buildings. It also hit close to most heavily populated area of the country, occurring only 10 miles from the capital, Port-au-Prince.
Further danger will come from aftershocks and landslides.
Edinburgh-based seismologist Brian Baptie said: "The combination of the earthquake's proximity to Port-au-Prince and its shallowness will result in the terrible damage we've seen. The more shallow an earthquake is, the greater the shaking at the surface. It's also the largest earthquake to hit Haiti in more than 100 years."
The last major one was in 1887 with a recorded magnitude of 7.2.
Prof Roger Searle, from the Earth Sciences Department at Durham University, said the magnitude seven quake was equivalent to the energy release of about half a megaton of TNT.
He said: "The earth's crust is a complex system and at the boundaries of the tectonic plates there are networks of faults separating lots of smaller blocks.
"As the plates move, stress gradually builds up until one part of this complex system gives way, and an earthquake occurs."