An earthquake measuring 5.1 on the Richter scale today rocked Assam, according to the Regional Seismological Centre. There was no immediate report of any damage or casualty, officials said here. According to the report of the Regional Seismological Centre at Shillong, the epicenter of the medium intensity earthquake was at a place 22 kilometers from Dhing in Nagaon district. The epicenter was located at latitude 26. 2 north and longitude 92.5 degrees east.