Seismologists are closely monitoring what they say is an unusual absence of aftershocks after a 5.4 Richter earthquake that shook the southern Peloponnese town of Kalamata early yesterday. The quake, which struck at 2.35 a.m., caused minor damage to property and resulted in one woman having a heart attack. Anna Valavani, 65, was in a critical condition in hospital yesterday. The epicenter was 7 kilometers (4.5 miles) northwest of the town, 165 kilometers (102.5 miles) southwest of Athens. According to Giorgos Stavrakakis, director of the Geodynamic Institute, the temblor occurred in the same seismic zone as the 6.2 Richter quake in 1986 which killed 26 people and caused major damage. «It is too early to make safe estimates, but the absence of aftershocks is unusual. We will have to wait two or three days before we get a clear picture,» he said. Patras University Professor Akis Tselentis warned Kalamata residents to avoid old buildings for the next few days.