Three great earthquakes and destructive tsunamis over the past four years is not enough to spare the region of another large earthquake, warns an international group of earthquake researchers in their paper published in the Dec. 4 issue of the journal Nature.
The first of the recent great earthquakes, a magnitude 9.2 in December 2004, produced the most widespread and destructive tsunami in living memory. The cause of that calamity was the rupture of a 1600-km-long piece of the Sunda megathrust, a 6,000-km-long active fault that dives gently landward from the seafloor a couple hundred kilometers offshore of Myanmar, Sumatra, Java, and Bali. The section that broke in 2004 is a northern portion, between southernmost Myanmar and Aceh province in Sumatra.
Only three months later, the next section to the south, offshore Aceh and North Sumatra, also ruptured suddenly. That 350-km portion, just north of the Equator, produced a magnitude 8.7 earthquake and a more modest tsunami.
Says Professor Kerry Sieh, one of the paper's authors and Director of the Earth Observatory of Singapore, Nanyang Technological University, "Before the 2007 earthquakes, we knew that a big section still farther south had not broken for the last two centuries. There was great concern that this patch would break. What we learned in this study is that only part of it did during the 2007 earthquakes."
After the 2004 and 2005 earthquakes, the only large, unbroken section of the megathrust off the coast of Sumatra was a 700-km portion south of the Equator, beneath the Mentawai Islands, a chain of large islands offshore from the major cities of Bengkulu and Padang.
"The great fault that runs along the eastern flank of the Indian Ocean has been the world's most energetic fault zone lately," says the paper's co- author, Danny Hilman Natawidjaja, of the Indonesian Institute of Science. "Nonetheless," he says, "one large section offshore Sumatra has st
|Contact: Esther Ang|
Nanyang Technological University