On Monday, the day the Nord Stream 1 and 2 gas pipelines saw substantial drops in pressure, a seismograph on the Danish island of Bornholm twice registered spikes that represented ground tremors, according to the German geological research centre GFZ.

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Up until 0003 GMT (2 am local time), the seismograph showed almost complete calm. Then, there was a spike that represented an earth tremor, followed by a persistent hissing pattern. At 1700, the sequence started all over again.

Politicians and security experts from Europe have proposed that sabotage may have been to blame for the pipeline rupture near Bornholm. GFZ refuses to comment on the possibility that the earthquakes were caused by an explosion, reported Reuters.

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Josef Zens, a GFZ official, stated that “there was a spike and then regular noise. We cannot say if that could be gas streaming out.”

On Monday afternoon, it was first reported that Nord Stream 2 had depressurized. After the second of the two spikes, there was a depressurization in the Nord Stream 1 pipeline, which was detected in the early evening.

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Following the detection of a leak on the neighbouring Nord Stream 2 pipeline, which led Denmark to impose a five nautical mile shipping restriction, the Swedish Maritime Authority issued an advisory over two leaks in the Nord Stream 1 pipeline.

A dispute over energy that is intensifying between Moscow and European towns has both pipelines at its centre. The major Western economies have suffered greatly as a result of this battle, which has also driven up gas costs and stimulated a search for alternate energy sources.