: Seismologists studying a magnitude 7.1 earthquake that occurred in Chile in 2011 say they have found that it actually comprised two ruptures on two separate faults. Another Chilean earthquake, which occurred in 2010 and was the fifth largest ever recorded, has also been found to have triggered a second large quake, of magnitude 7.7, just 12 seconds later. However, in both cases the second quake went undetected by seismic monitoring systems. According to a paper
published in Nature Geoscience
by Stephen Hicks and Andreas Rietbrock of the University of Liverpool in the UK, the South American continental margin is one of the most seismically active regions in the world and may commonly experience similar hidden quakes.
One danger is that such so-called earthquake doublets can trigger much larger tsunamis. “Such triggered events dramatically complicate potential earthquake impact assessments and tsunami early warning systems,” says Rietbrock.