Awakening a fault line within

摘要

A large fault section off Sumatra that had been seismically dormant for more than 30 years has recently reawakened, thanks to a series of large earthquakes in the area during the past decade. Kelly Wiseman at the University of California, Berkeley, and her team linked data derived from the Global Positioning System on surface motions from Sumatran stations with the known geometry and mechanisms of recent quakes. They found that a 900-kilometre-long 'backthrust' - arising from the longer Sunda megathrust fault that caused the 2004 Indian Ocean earthquake and tsunami - produced a moderate quake in 2005 and another in 2009. If a rare faulting event were to rupture the newly active thrust, it could produce a quake on the order of magnitude 8.5, and, potentially, a large tsunami, the authors suggest.