In a study published in Nature Geoscience, University researchers analysed in detail the seismic wave recordings from 2 January 2011 when an earthquake of magnitude 7 occurred in Chile along the plate boundary separating the subducting Nazca plate from the South American continent. They discovered that just 12 seconds later and 30 km further offshore, a second rupture of a similar size, which was un-detected by national and global earthquake monitoring centres, occurred along an extensional (pull-apart) fault in the middle of the South American plate beneath the Pacific Ocean. Liverpool seismologist, Professor Andreas Rietbrock, said: "Real-time global seismic monitoring and early warning events have come a long way and it is possible for a magnitude 5 or greater earthquake to be detected within a matter of minutes.