Megathrust earthquake could hit Asia 'at any time'
By Tamsin Osborne A devastating “megathrust” earthquake could occur at any time off the Indonesian island of Sumatra, according to new research. Previous quakes have failed to release all of the energy that has built up over hundreds of years, leaving the fault zone vulnerable to another large earthquake. Using GPS, field measurements, radar data and seismological records, a team of international researchers investigated the parameters and reconstructed the events of two massive earthquakes, measuring 8.4 and 7.9 on the Richter scale, which occurred in the Mentawai area in 2007. Previous models of how earthquakes work had suggested that the same fault would rupture in the same way and at regular, predictable time intervals. But the researchers found that the 2007 quakes ruptured only a fraction of the area affected by the giant 1833 earthquake, indicating that a tectonic plate boundary can rupture in different patterns depending on local differences in stress. “What we see here is that the 2007 earthquake had at least a very big overlap with the 1833 earthquake, but it was very much smaller; in other words, it was an entirely different earthquake,” says John McCloskey, a geophysicist at the University of Ulster, UK. The GPS data enabled the researchers to create a map of the fault zone, showing which parts were locked tight and which parts were slipping freely. This allowed them to estimate where the most strain has built up, and where the next big rupture is most likely to occur. The results suggested that the 2007 events released only a quarter of the energy that had accumulated since 1833, leaving enough pent-up energy to trigger another giant earthquake at any time. This event could be anything between magnitude 8.2 and over 9, says McCloskey. The earthquake that led to the devastating Asian tsunami of 2004 occurred in a different part of the same fault and measured between 9.0 and 9.3. The 2004 event is thought to have increased the strain on the Mentawai region, making an earthquake there even more likely. The potential devastation that such an earthquake could cause is horrifying, says McCloskey. “There’s a city called Padang, with 840,000 people, facing right into the place where we know the fault hasn’t broken since 1797,” he says. “It’s more stressed now than it was in 1797, so it could be quite soon.” Since the 2004 event, a tsunami warning system has been put in place to prepare the region for further quakes. But, according to McCloskey, it will be next to useless for this earthquake, since it will occur so close to inhabited areas that there will be no time for advance warning. “The ground’s going to shake so hard during this earthquake that you don’t need a tsunami warning system,” he says. When the next big earthquake strikes, says McCloskey, people living nearby will have less than 30 minutes to get to high ground. Journal reference: Nature, DOI: