Earthquake experts said yesterday that they are closely monitoring heightened seismic activity in northern Greece after a quake and three aftershocks rocked Thessaloniki over the weekend. Sunday’s earthquake, measuring a moderate 4.4 on the Richter scale was felt in Thessaloniki as its epicenter was in the nearby Lake Volvi area, some 50 kilometers (80 miles) east of the city. Seismologists, however, are concerned that it came so soon after five minor quakes were felt in the area on September 12. «There is no doubt that there has been a rise in activity in the Serbo-Macedonian zone recently, which we are studying and monitoring in a number of ways,» Giorgos Karakaisis, professor of seismology at Aristotle University, told Kathimerini. The Serbo-Macedonian zone stretches from southern Serbia to Halkidiki. Karakaisis said it was not possible to make any accurate predictions about what might happen in the future but added that the recent series of quakes was not similar to the one that preceded the 6.5 Richter earthquake that hit Thessaloniki in 1978, killing 45 people.