Scientists investigating the attack on the Nord Stream pipelines have revealed key new details of explosions linked to the event, which remains unsolved on its first anniversary. Researchers in Norway shared with the Guardian seismic evidence of the four explosions, becoming the first national body to publicly confirm the second two detonations, as well as revealing a detailed timeline of events. The recently discovered additional explosions took place in an area north-east of the Danish Baltic island of Bornholm about seven seconds and 16 seconds after the two previously known detonations. Using information from seismic stations in northern Europe and Germany, including the Swedish National Seismic Network and Danish stations on Bornholm, seismologists deployed advanced analysis techniques to observe and pinpoint the blasts. Seismologists at Norsar, Norway’s national data centre for the comprehensive nuclear test ban treaty (CTBT), told the Guardian they had so far found a total of four explosions – one south-east of Bornholm and three north-east of the island. Two clear seismic events, named Event S and Event N, were identified on 26 September 2022, soon after the attack. The first, on Nord Stream 2, occurred at 02:03:24 (UTC+2), and the second, on Nord Stream 1, at 19:03:50 (UTC+2). Norsar said there could potentially be further explosions buried in the data. The explosions made holes in both Nord Stream 1 pipelines and one of the Nord Stream 2 pipelines. By November last year, Swedish investigators had confirmed that the breaches were caused by man-made explosives. Investigations are continuing, but officials quoted in the US and German press have said the evidence points towards a Ukrainian-backed group, or a pro-Ukrainian group operating without the knowledge of the leadership in Kyiv. German investigators have focused on a 51ft rental yacht called the Andromeda, which was hired by a mysterious crew of five men and one woman, at least some of whom were travelling on false passports. Der Spiegel, which recreated the Andromeda’s journey, quoted investigators as saying the evidence all pointed at Kyiv’s involvement. There is debate, however, over whether a small crew of divers operating from a pleasure yacht would have been capable of carrying out the difficult, deep and slow dives necessary to place the explosives. A leaked US defence document, reported by the Washington Post, showed the CIA had been tipped off by an allied European agency in June 2022, three months before the attack, that six members of Ukraine’s special operations forces were going to rent a boat and use a submersible vehicle to dive to the seabed using oxygen and helium for breathing, in order to sabotage the pipeline. But the leaked US document said the planned operation had been put on hold. Other reports in the Scandinavian media have pointed to a cluster of Russian ships, with their identifying transponders turned off, in the vicinity of the blast sites in the days before the explosions. The Nord Stream pipelines are operated by two companies, Nord Stream AG and Nord Stream 2 AG, both majority-owned by the Russian state energy company Gazprom. Nord Stream 1 and 2 are both twin pipelines, and together they bring up to 110bn cubic metres of gas annually from Russia to Germany. Nord Stream 1 went into operation in 2012. Nord Stream 2 was completed in September 2021 but has never transported any gas. From the outset it was mired in controversy in the face of adamant opposition from German allies, in particular the US and Poland, who both believed the Germans were making themselves and much of the rest of Europe hostage to Russian energy supplies. The US made clear that bilateral relations would be badly affected if Nord Stream 2 went into operation. Once the full-scale invasion of Ukraine began, all talk of opening the pipeline was shelved. The newly discovered events, named NB and NC, took place about seven seconds and 16 seconds after the event previously known as Event N, which they now refer to as NA. Investigations by Denmark, Sweden and Germany are understood to be planned for publication in a joint study with Norsar. Authorities for all three countries declined to comment on the investigations. In July, the UN security council heard investigators had found traces of undersea explosives in samples from a yacht, but that they were unable to reliably establish the identity or motives of those involved or whether it was the work of a specific country. Using information from a number of seismic stations in northern Europe and Germany, including the Swedish National Seismic Network and the Danish stations on Bornholm, seismologists used advanced analysis techniques to observe the additional two explosions. According to their calculations, the second and third explosions (NA and NB) were 220 metres apart from each other (with the third west of the second) and the fourth was several kilometres south-west of the second. Andreas Köhler, a senior seismologist at Norsar, said the distance between NA and NB “fit very well with the distance between both pipelines of Nord Stream 1 at the westernmost gas plume location northeast of Bornholm.” Nord Stream 1 and Nord Stream 2 both have two pipelines each. The location of the final explosion, however, is less clear because there are less station observations. “This best fits an explosion on the Nord Stream 1 pipeline, but we cannot exclude a location at Nord Stream 2,” said Kohler. Analysis of the source mechanism from the signals showed they were generated by explosive devices. Based in Kjeller, near Oslo, Norsar monitors events across the world including nuclear testing in North Korea, the impact of CO2 storage on the Norwegian continental shelf and conflict zones such as Ukraine. It takes 10 minutes for shock waves to reach them after a nuclear test in North Korea, with location accuracy of 150-200 metres, leading to the claim that it is “10 minutes from Kjeller to North Korea”. The war in Ukraine has marked a significant breakthrough for Norsar in terms of the potential use of seismology in conflict monitoring. “The technology that is used to find explosions the other side of the globe can also find explosions closer to home,” said its chief executive, Anne Strømmen Lycke. It started monitoring Ukraine for the Civil Radiation Authority due to concerns of radioactive landfall over Norway after the 1986 Chernobyl disaster. It monitors bombing around the power plant on a continuing basis and has been able to contribute evidence to the UN truth commission. In June, its scientists were able to confirm the time and location of reports of two explosions at the Kakhovka dam using data from seismic stations in Romania and Ukraine. “It’s amazing, the accuracy of the observation and the use of it. The UN truth commission for Ukraine has contacted us to ask us to verify some events, among them the Kakhovka dam, so they are interested in having these cold data as basis for their considerations.” Norsar is also investigating whether its technology could be used in the future to monitor ceasefires. “We know that we could see, based on frequency content and signal difference, between different helicopter types and likely also different weaponry types,” Strømmen Lycke said. “And that could be something to verify and then you could actually monitor and trace after unravelling who did what. I suppose that is why the UN truth commission is interested in these things.”