At about 20:00 on 21 January 1973, a series of small tremors began to occur around Heimaey. They were too weak to be felt by the residents of the island, but a seismic station away, near the mainland, recorded over 100 large tremors between 01:00 and 03:00 on 22 January that appeared to be emanating from south of Heimaey. The tremors continued at a reduced rate until 11:00 that day, after which they stopped until 23:00 that evening. From 23:00 until 01:34 on 23 January, seven tremors were detected that grew shallower and more intense, while the epicenter moved closer to the town of Vestmannaeyjar.