COPENHAGEN, Denmark -- Officials in Denmark are puzzled by four small tremors that were recorded this week off a northeastern Danish island in the Kattegat sea.
The Geological Survey of Denmark and Greenland (GEUS) said it had detected the tremors on Tuesday and Wednesday, adding that each time there were two tremors approximately 30 seconds apart.
The shakes were recorded in international waters off the Danish island of Laesoe. They were measured between 0.7 and 0.9 on the Richter scale, and occurred at 10.41 a.m. and 03.26 a.m., respectively, GEUS said.
The seismological agency said in a statement Thursday believe they were "natural earthquakes.”
“However, the tremors are very small, and since the signal is so weak, after further analysis, GEUS cannot determine with certainty what is causing the seismic signals.”
The agency said the tremors have been detected in areas where there is no Danish critical infrastructure, and that the authorities were closely following the situation in the waters in and around Denmark.
The tremors came after blasts last month damaged two Russian-built natural gas pipelines in the Baltic Sea — two leaks were reported off Sweden and two off Denmark. All were in international waters.
The governments of Denmark and Sweden previously said they suspected that several hundred pounds of explosives were involved in carrying out a deliberate act of sabotage. The leaks from the Nord Stream 1 and 2 pipelines discharged huge amounts of methane into the air.
The Kattegat is off Sweden and Denmark, at the entrance to the Baltic Sea.