An earthquake of moderate intensity shook the Indonesian island of Sumatra on Wednesday morning, according to the Met Department.The temblor, measuring 5.7 on the Richter scale, occurred at 12 am off the west coast of northern Sumatra, it said.The epicentre of the earthquake was at 2.3 degree north latitude and 96.4 degree east longitude.Details of any damage or casualties were not immediately known.