Seismologists in the Nordic and Baltic countries said on Sunday they had detected shock waves associated with an explosion at the Balticconnector gas pipeline before the pressure suddenly dropped, but the data was insufficient to determine whether explosives were used, Reuters reported.

The new information comes after the Finnish police unit investigating the incident said on Wednesday that the damage to the gas pipeline was apparently the result of “mechanical force” and not an explosion.

But seismologists from Norway’s NORSAR institute have now announced that, after analyzing data collected in Finland, they have detected a “probable explosion” near the pipeline shortly before the pressure drop reported by Gasgrid, the operator of the Finnish gas transmission system.

Seismologists have noted that waves measured after explosions tend to leave distinctive signals different from those caused by earthquakes.

“We know it wasn’t an earthquake, and we know it was an explosion, but what caused the explosion needs further investigation,” NORSAR director general Ann Strommen Lieke told Reuters.

“We have seen that there are suggestions that the ship may have pulled the pipeline and that this led to the hole and the subsequent explosion, but it is too early to say whether that happened,” she added.

Finland’s National Bureau of Investigation also said Wednesday that footprints had been found on the seabed near the pipeline and that it was analyzing ship movements in the area. Finnish investigators clarified that one of the tracks traced refers to an explosion caused by damage to the ship’s anchor.

What do the data of seismologists indicate about the incident that damaged the Balticconnector gas pipeline

NORSAR said the detected seismic signal was only one degree on the Richter scale and was much weaker than the minor earthquakes or larger explosions that damaged the Nord Stream 2 pipeline last year.

According to the seismological institute, the corresponding explosions were recorded at a magnitude of 2.3 on the Richter scale.

“We see a seismic signal coming into the Gulf of Finland at that time that has some characteristics that at least make an explosion possible or likely,” said seismologist Björn Lund of Uppsala University in Sweden.

Jari Kortström, another seismologist at the University of Helsinki, said the seismic data “could indicate an explosion,” while Estonian seismologist Heidi Soosalu said the signals likely indicated a “man-made event.”

NORSAR also said Sunday’s seismic signal likely came from an area less than 5 kilometers from the Nord Stream gas pipelines.

“Maybe we’re lucky that it (without the explosion) didn’t damage the Nord Stream gas pipelines even more,” said Lieke, CEO of NORSAR.

The Balticconnector pipeline connects the cities of Inkoo in Finland and Padiski in Estonia, its 77-kilometer underwater section along the Gulf of Finland, an area of ​​the Baltic Sea that stretches eastward to Russian territorial waters and the port of St. Petersburg.

Finnish authorities said earlier on Tuesday that an “external person” appeared to be involved in the incident that damaged the gas pipeline, but did not name any suspects. Estonia is also investigating the cutting of an underwater communications cable, which appears to have been cut in the same incident.

NATO Secretary General Jens Stoltenberg said that if it is proven that the damage to the Balticconnector gas pipeline was the result of a deliberate attack, NATO’s response will be “united and decisive.”