Tsunami unravelled
A NEW understanding of future earthquakes, especially in South Asia, has emerged from studies of the tremor that caused the devastating December 26, 2004 tsunami in the region. The findings of three studies on the Sumatra-Andaman quake have been published in the latest edition of the journal Science (May 20, Vol 308, No 5725).
Scientists remark that it was the first major earthquake to be observed with modern instruments, satellites, digital seismometers and global positioning systems. "We've never had such comprehensive data for a great earthquake,' says Thorne Lay, a geologist at the University of California, usa, who worked on two of the studies.
Besides the December quake, which was the most powerful in the past 40 years, the scientists also studied the one that struck almost the same area just three months later on March 28, 2005. With an 8.7 seismic moment magnitude (a measure of total energy released by an earthquake), it became the second largest earthquake over the same period.
While one study provides an overview of the two earthquakes, another concentrates on the processes involved in the rupture of the fault. The third study illustrates how the earthquakes caused the whole planet to vibrate with free oscillations, similar to what happens when a bell rings.
What happened According to the first study, the Sumatra-Andaman quake lasted almost 10 minutes, unlike most large earthquakes that last only a few seconds. It measured 9.3. The ground shook more than 100 times harder than it did during the 1989 California Loma Prieta earthquake