Two days of Earth and human-generated vibrations prior to and during the 2020 lockdown, Dublin, Ireland (acceleration 120x)

Below: Stereo spectrograms of the upper range of the secondary microseism (the diffuse noise wavefield at the bottom of each channel’s spectrogram) and of the human-generated vibrations on two separate Mondays, 17 February and 20 April, 2020. Each seismogram was recorded from midnight to midnight.

These low-frequency signals are inaudible to the human ear. They include the ocean-wave-generated vibrations within the secondary microseism and the seismic signals from the road traffic and industrial activity. Accelerated by 120x, the audio presents two symphonic soundscapes: continuous vibrations of machines are transformed into tones of musical quality. The DSB seismic station is situated in the Glenasmole Valley in the Dublin Mountains. The nearby Bohernabreena Waterworks, established in the 1880s, employ giant pumps to supply approximately 35,000 households in South Central Dublin with water. This operation probably creates the most prominent note heard in both recordings, seen in the spectrograms by the brightest continuous line starting around 6.30 a.m. and continuing (with distinct breaks) into the late afternoon. This musical ‘pedal point’ is joined occasionally by other tones and the multitude of shorter sonic events that are scattered throughout the entire duration of the seismograms.

These stereo tracks are renderings of the 3 components of the motion of the ground at a 236 m elevation, south of Dublin, Ireland. The seismograms were recorded on 17 February 2020 and 20 April 2020 respectively, by the seismic station DSB of the Irish National Seismic Network, located at 53.25°N, 6.38°W.

Bandpass filtering was applied in the audio domain to reduce the secondary microseism noise and enhance the sonic experience of the human-generated sounds.

The secondary microseism in the above example is very active. February 2020 was an exceptionally wet and windy month, with two Atlantic storms, Ciara (9 and 10 February) and Dennis (15 and 16 February) sweeping over Ireland (see https://www.met.ie/climate-statement-for-february-2020). The human-generated vibrations are also very prominent, showing the typical activity on a busy Monday in the Dublin region.

The secondary microseism appears a lot less active here compared to the 17 February seismogram, due to a spell of splendid weather in this period.

Like in the pre-lockdown example, the main feature of this seismogram appears to be the continuous operation of the giant water pumps from the nearby Bohernabreena Waterworks, which were still active to supply households in South Central Dublin with water during lockdown. Due to the much-reduced traffic sounds here (work and leisure travel were largely absent), one can see more clearly the upper harmonics of the water pump vibrations above the fundamental note.