John McCloskey and his colleagues at the University of Ulster analyzed data from the 2004 Sumatra-Andaman earthquake and found two zones of increased seismological stress in the surrounding area. The first region lies in the Sunda trench, which is a 50-kilometer-long section off the northern tip of Sumatra, and the second is on the Sumatra fault, which runs under the length of the island and ends near Banda Aceh. "Our results show a stress increase of up to five bars in the Sunda trench next to the rupture zone and a strong positive loading of nine bars for 300 kilometers of the Sumatra fault," McCloskey remarks. As a point of comparison, it is believed that the recent Izmit earthquake in Turkey, which measured a magnitude 7.4, was triggered by stress increases of about two bars over an area of 50 kilometers.
The authors report that their results suggest an earthquake of magnitude 7-7.5 on the Sumatra fault "would seem to represent the greatest immediate threat." From preliminary data collected on Wednesday's quake, it remains unclear whether the faults analyzed in this study were involved or whether it occurred on a fault that is not as well categorized. "Every earthquake that occurs [in the region] is going to relieve some of the stress," notes John Bellini, a geophysicist with the United States Geological Survey. But because of the logarithmic nature of the Richter scale, he notes, "you'd need 1,000 earthquakes of magnitude five to release as much as one magnitude seven [quake]." McCloskey and his colleagues note that their findings underscore the need for a warning system: "It is vital that disaster fatigue does not delay the implementation of the Circum Indian Ocean Tsunami Warning System."
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