Tsunami Alert Lifted

By Colin Hinshelwood 12 April 2012

India, Thailand and Burma were among the Asia-Pacific nations that lifted a tsunami warning on Wednesday night after fears subsided that a natural disaster was imminent following a major earthquake off the coast of northwestern Indonesia.

The 8.6-magnitude earthquake occurred at 15:38 local time (08:38 GMT) some 435 km off the coast of Aceh, close to the epicenter of the Dec. 26, 2004, earthquake which registered 9.1 on the Richter scale and caused a massive tsunami across the Indian Ocean, ultimately killing more than 230,000 people in 14 countries.

Experts say a tsunami did not occur on Wednesday because the subduction—the process by which tectonic plates move against each other—was a “strip-line quake,” moving horizontally, as opposed to the vertical clash of plates that occurred in 2004.

Roger Musson, a seismologist at the British geological survey, was quoted by the Associated Press as saying that initially he’d been “fearing the worst.”

“But as soon as I discovered what type of earthquake it was … I felt a lot better,” he said.

Panic broke out across Southeast Asian coastal areas after the initial quake, which could be felt in Bangkok, Rangoon, Singapore and India. It was followed within the hour by an equally strong aftershock.

In western Sumatra, a four-minute tremor sent residents scrambling from their homes in chaos, heading for higher ground. In Aceh province, where 170,000 people were killed in 2004, patients were wheeled out of hospitals, some still lying in their beds with drips attached to their arms. One hotel guest was reported slightly injured when he jumped out of his window.

In Thailand, witnesses reported a “sliding” or “wobbly” tremor, as opposed to what most people described as a “rumbling” or “vibrating” shudder in 2004.

In Krabi, the governor quickly ordered all beaches evacuated, and urged all residents and tourists to seek higher ground. In Phuket, residents drove to the hills, some staying there until well into the night, and long after the projected time of arrival for the wave had passed.

In Thailand’s idyllic islands of Koh Phi Phi—which were leveled in the 2004 tsunami—hotel staff, fishermen and tourists reportedly dropped whatever they were doing after the initial tremor, and clamored for high ground in a state of unreserved panic.

Sirens were sounded along coastlines and warnings spread like wildfire by mobile phones and social media such as Facebook.

Countries all along the Indian Ocean—from Australia and India to as far off as Africa—received alerts from the Pacific Tsunami Warning Center in Hawaii saying they should prepare for the possibility of “seismically charged waves.”

Hour later the tsunami warnings were lifted, and damage from the tremors was minimal — something experts attributed to the unique nature of the fault line.

Associated Press reported that the only wave to hit was less than 30 inches (80 centimeters) high, rolling into Indonesia’s emptied coastline.

The US Geological Survey said the first 8.6-magnitude quake was a shallow 14 miles (22 km), striking in the sea 270 miles (435 km) off Aceh’s coast—making it the sixth-largest quake in the last half-century.

Just as the region was sighing relief, an 8.2-magnitude aftershock followed, again causing only slight damage.

However, the World Meteorological Organization (WMO) said that communication systems set up after the 2004 tsunami appeared to have been successful.

“Our records indicate that all the national meteorological services in the countries at risk by this tsunami have received the warnings in under five minutes,” said Maryam Golnaraghi, the head of WMO’s disaster risk reduction program, as reported by Associated Press.

Seismic experts on Thursday said that aftershocks from Wednesday’s quake are likely to persist for weeks or months, and can be as strong or stronger than the initial temblor, though they mostly weaken over time.