The tremor was centered somewhere near the Ekofisk oil field, about 185 miles southwest of Norway's southern tip. It had a magnitude of 4.0, enough to cause moderate damage although none was reported.
In the 30 years since Ekofisk began production, the seabed under Norway's oldest offshore field has sunk by about 26 feet as petroleum was pumped out of the subsea reservoirs. The area has about 25 platforms and other offshore structures.
Conrad Lindholm, of the Norwegian Seismic Array monitoring station, said the event was registered at 11:34 a.m. (0943 GMT) and could have been either an earthquake or the collapse of an oil reservoir.
He said it lasted for a minute -- unusually long for an earthquake in Norway.
“We can't tell for sure. All we can say is that there was a seismic event and that it had a magnitude of 4.0,” he stated.
Ekofisk is operated by the Norwegian division of Phillips Petroleum.
Phillips spokesman Ingvar Solberg reported that no injuries occurred among the 852 workers on the platforms and no damage had been reported and production was normal. It was reported that some platforms rattled and swayed and some loose items fell down.
Phillips raised most Ekofisk platforms in 1987 to counter the seabed subsidence and now injects water to replace the roughly 350,000 barrels per day of oil pumped out.
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