Seismologists suspect explosions damaged undersea pipelines that carry Russian gas

Two undersea leaks that began in the Russian-owned Nord Stream gas pipelines on Monday were likely caused by powerful underwater explosions, according to Swedish and Danish seismographic data.

It is "very clear from the seismic record that these are blasts," Björn Lund‬, director of the Swedish National Seismic Network at Uppsala University told NPR in a phone interview. "These are not earthquakes; they are not landslides underwater."

German and Danish officials said both the Nord Stream 1 and Nord Stream 2 pipelines showed sudden losses of pressure late Monday, which they said could only be caused by a leak from large holes in the pipelines.

Neither of the pipelines are active, as Russia has cut gas deliveries in them, but both were filled with natural gas when the drop in pressure occurred. Russian energy giant Gazprom, a state entity, owns a controlling interest in both pipelines.

Denmark’s Prime Minister, Mette Frederiksen, said on Tuesday that her government suspected the leaks were deliberate actions.

Danish authorities reported the location of the Nord Stream 1 leak as northeast of the Baltic Sea island of Bornholm, and the Nord Stream 2 leak as southeast of the island. German media, quoting unnamed security officials, say it's possible the leaks are a result of an act of sabotage, as it's extremely rare for undersea, concrete-coated steel pipes to break on their own. Authorities have halted all shipping in the area around the leaks.

Lund says both the Swedish network and the Danish Seismic Network picked up the explosions on Monday. The first blast occurred at 2:03 a.m. Swedish time, and a second, larger explosion occurred at 7:04 p.m. "Preliminary estimates would say that this is at least equivalent to 100 kilograms of dynamite," he says.

Lund says the seismic data was able to pinpoint the second blast to within just a few kilometers of the location the Swedish Maritime Authority gave as the site of the second leak. “We’re not spot on, but we’re fairly close to the area of the leakage,” he says.

Lund says there's no natural event that could have created such unique seismic signatures less than 24 hours apart. "There's nothing I could come up with that would produce this," he says.

Instead, he says that the seismic events closely resembled what the network has detected in the past when the Swedish Navy has conducted training exercises using depth charges and undersea mines. Lund says he has notified the Swedish Armed Forces of his findings; they did not immediately respond to NPR’s e-mailed request for comment.

It remains unclear who might have conducted the possible sabotage. On Twitter, H.I. Sutton, an expert on submarine warfare and a writer for U.S. Naval Institute News pointed out that the relatively shallow depth at which the explosions took place would be reachable by divers or unmanned underwater vehicles.

Speaking on Tuesday, U.S. Secretary of State Anthony Blinken acknowledged the possibility that the damage to the pipelines was deliberate, then added: "If it is confirmed, that's clearly in no one's interest."

NPR diplomacy correspondent Michele Kelemen contributed to this report.

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