The 2012 Indian Ocean earthquakes

A magnitude 8.6 (Mw) undersea earthquake struck south of the Indonesian province Aceh on 11 April, 2012, at 15:38 local time, followed by a magnitude 8.2 aftershock 2 hours later. These large earthquakes were produced by horizontal slip on the undersea faults. Thanks to the lack of vertical movement of the seafloor, no tsunamis were generated.

The rich sound in this stereo track comes from a combination of 3-component seismograms recorded by all the stations of Ireland Array, recording across Ireland. The stronger main event is followed by a similarly structured sequence of waves of the main aftershock. The recording is accelerated by a factor of 9600, which increases the frequency of the signal by the same factor and brings it into the audible frequency range. The recording is then “stretched” by a factor of 80, so that the different waves can be distinguished in time and heard clearly.