Earthquakes
Seismograms of earthquakes have a particular, recognizable structure. The high-frequency first arrivals (primary, or P waves) are followed by lower-frequency secondary (S) waves, and then by the energetic, low-frequency surface waves, as in these examples. The lowest-frequency surface waves usually arrive earlier than the higher-frequency ones, which produces an upward glide (glissando) from low to high pitch.
The concluding part of the seismogram is the Coda, composed of numerous scattered waves arriving from different directions.
---
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 Mw = 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 wave, the long coda of the seismogram shows its own, original musical style, with moving, somber notes and harmonies.
Credit for Video and Article
David Stalling
https://www.soundsoftheearth.ie
