Seismologist warns of more huge quakes off Sumatra island
The Jakarta Post, Jakarta, Padang
A prominent seismologist said he could not rule out the risk of a third big quake off the Indonesian island of Sumatra, where two massive temblors have occurred in just three months.
"The probability of a third quake in the coming months and years, cannot be excluded," Mustapha Meghraoui, in charge of active tectonics at the Institute for Planetary Physics in Strasbourg, eastern France, told Agence France Presse.
"The theory is that this particular region has seismic cycles of between 150 years and 200 years. The Dec. 26 event caused extreme disruption, and one possibility is of a cascade of quakes," Meghraoui said.
Monday's 8.7-magnitude quake -- one of the biggest in a century -- came just over three months after a 9.0 event further to the north which unleashed the tsunami that scoured the coastline of the northern Indian Ocean, killing more than 273,000 people.
The two events occurred in the subduction zones where plates of the Earth's crust overlap, bumping and grinding.
The Dec. 26 event occurred at a stress point where the Indian plate slips under a tongue called the Burma microplate.
That quake unleashed a huge amount of energy to a Sunda Trench, the undersea fault that runs to the west of Sumatra, where there were big quakes in 1833 and again in 1862.
In this region, the Indian Ocean is sliding beneath Indonesia at the rate of seven centimeters (2.8 inches) a year, he said.
But this is not a smooth movement. Tension builds up as the plates jam, and when the tension is suddenly and violently released, the result is an earthquake.
Although tsunami alerts were issued after Monday's event, no big wave occurred -- or more exactly, nothing as big as the wall of water up to 10 meters high that caused so much devastation on Dec. 26.
The reason, said University of Ulster seismology professor John McCloskey, was Monday's quake was around 12 to 15 times smaller in magnitude than the Dec. 26 behemoth.
"That's crucial, because the bigger the energy released, the greater the chance that the seabed will move," McCloskey was quoted as saying by AFP.
And it occurred relatively far below the surface -- at a depth -- of about 30 kilometers, according to the U.S. Geological Survey (USGS).
In a study published on March 17 in the British science weekly Nature, McCloskey's team had warned of the potential for a very large, imminent quake of up to 8.5 magnitude, either on the Sumatran fault, which slices across the Indonesian island, or in the Sunda Trench as a result of the Dec. 26 disaster.
Meanwhile, earthquake expert Danny Hilman Natawidjaja of the Indonesian Institute of Sciences (LIPI) shared Meghraoui's view that another big earthquake might occur in the future near Nias Island.
He therefore suggested that the government in the nearest city, including the densely populated city of Padang, West Sumatra province, embark on measures to mitigate the impact of a possible tsunami. Among the mitigation measures proposed are the establishment of evacuation lines, tsunami evacuation training especially for students and children and the establishment of a tsunami early warning system.