PARIS, March 30: In a reassessment of the December 26 earthquake that unleashed the Indian Ocean killer tsunami, scientists say the temblor measured 9.3 on the Richter scale — more than twice as powerful as originally estimated and the second biggest quake ever recorded. The quake split the ocean floor northward from Sumatra along 1,200 kilometre, twice as long as previously thought, according to their research, which appears on Thursday in Nature, the weekly British science journal.

The event released so much strain along this particular part of the fault that in theory there should be no quake of similar magnitude, or a similar tsunami, there for another 400 years, said geologists Seth Stein and Emile Okal of Northwestern University, Illinois. But farther south, it is a different picture.

The scientists — who wrote before last Monday’s quake, which also struck western Sumatra — warned with uncanny prescience that “a great earthquake” with the potential to generate a large tsunami remained a threat south of the December 26 site.

The December 26 quake occurred off northwestern Sumatra, at the nexus where the Indian plate of the Earth’s crust is sliding under a tongue-shaped sliver called the Burma microplate.

It was initially thought to be 9.0 on the Richter scale. But an evaluation of very low frequency data from seismograms shows that the quake was in fact 9.3 magnitude.

As the Richter scale is logarithmic, the difference between 9.3 and 9.0 is 2.5 times, the study said. Only one measured quake has been bigger: a 9.5 event that struck Chile in 1960.—AFP