Haiti quake caused by unknown fault, say scientists

LONDON - A team of researchers has found that a previously unmapped fault was responsible for the devastating Jan. 12 earthquake in Haiti and that the originally blamed fault remains ready to produce a large earthquake.

Eric Calais, a Purdue University professor of earth and atmospheric sciences, led the team that determined the earthquake’s origin is a previously unmapped fault, which they named the Leogane fault.

The newly discovered fault runs almost parallel to the Enriquillo fault, which was originally thought to be the source of the earthquake, he said.

“This means that the Enriquillo fault is still capable of producing large earthquakes and that Haiti has to adapt to this seismic hazard,” said Calais, science adviser for the United Nations Development Program in Haiti.

“The fault system is more complex than we originally thought, and we don’t yet know how the January earthquake impacted the other faults.

“Preliminary measurements indicate that the Enriquillo fault did not release any accumulated seismic energy and, therefore, remains a significant threat for Haiti, and Port-au-Prince in particular. We need to investigate the fault system further to be able to determine where the next earthquakes might occur and how large they could be,” he said.

The team analysed data they recorded before the Jan. 12 earthquake and new measurements taken after the event.

Andrew Freed, paper co-author, said the absence of any surface rupture was the first clue that the earthquake did not happen along the Enriquillo fault.

“We did find other physical changes that we expected after an earthquake of that magnitude, but in entirely the wrong location to have come from the Enriquillo fault,” said Freed.

For instance the team found that the epicentre area rose by a little more than half a meter and that the earthquake caused contraction of the Earth’s crust opposite of what would be expected from the Enriquillo fault, he said.

The team used global positioning system equipment and radar interferometry to measure how the ground moved during the earthquake, which provides insight into what is happening as much as 20 kilometres below the surface.

The team then used a computer model to determine what characteristics the source of the earthquake must have in order to produce the observed changes.

The findings were detailed in the Nature Geosciences. (ANI)