The Tohoku Earthquake

The catastrophic Tohoku earthquake occurred at 14:46 Japan standard time (05:46 UTC) on 11 March, 2011. The largest earthquake ever recorded in Japan (magnitude M_w=9.1), it occurred undersea, 70 km to the east of the Tohoku region, and lasted around 6 minutes. The earthquake triggered a tsunami that reached heights of up to 40 metres and travelled up to 10 km inland.  Nearly 20 thousand casualties have been reported. The tsunami caused the Fukushima Daiichi nuclear disaster, with the discharge of radioactive water in Fukushima and hundreds of thousands of residents evacuated.

This seismogram is a recording of the Tohoku earthquake made thousands of kilometres away, at the Ireland Array seismic station IA003, Birr Castle Demesne, Co Offaly, Ireland. The seismogram shows the vertical component of the ground motion (up and down movements of the ground). The recording is accelerated by a factor of 4320, 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 40, so that the different waves can be distinguished in time and heard clearly.

Following the energetic arrivals of P, S, and surface waves, the long coda of the seismogram makes music in its own original style, with moving, somber notes and harmonies.