The earthquake was assigned X — Extreme — on the Mercalli intensity scale, the highest category before Catastrophic. Six people died inside a five-story reinforced concrete apartment building that collapsed. Six others were killed by falling debris elsewhere in the city. One person was crushed. One died of a heart attack. An infant died of suffocation. Another infant died of injuries. At the Holy Monastery of Velanidia, southeast of the city, three people perished when the monastery's old defensive towers collapsed. In the village of Elaiochori, four more people died when an old stone building fell. In all, at least 20 people were killed and 330 injured, including 83 with serious injuries. Each of these deaths happened in a city of ordinary people going about an ordinary Saturday evening.

Kalamata sits at the border of the Messinian valley and the Messenian Gulf, in a geological structure called a graben — a block of the earth's crust that has subsided between parallel faults. To the east, the Taygetus mountains rise sharply, separated from the coastal plain by a series of normal faults, including the Kalamata Fault: a northwest-dipping fracture that strikes north-northeast and had never, before 1986, been associated with any earthquake or surface rupture. Geologists believed it had formed during the Quaternary period. On 13 September it ruptured along its northern extent all the way to the surface, leaving visible fault scarps east of the city, some measuring up to several centimeters in vertical height, running through terraced olive groves near rocky outcrops. The ground itself had cracked open.

Power went out across Kalamata as the shaking stopped. Communication services were disrupted. Rescuers moved immediately to two specific buildings — the collapsed apartment and a two-storey house where people were trapped. Greek Army personnel, police, and firefighters arrived alongside civilian rescuers. Four survivors were pulled from the apartment building in the first hours; seven more were rescued the following afternoon. Rescue teams from France and Germany came to assist. Recovery was slowed in places by the presence of onlookers, friends, and family members of the trapped who had rushed to the sites — understandable human responses that nonetheless complicated the work. At the city's jetty, cracks up to several centimeters wide appeared in the walls, and sections partially detached from the main structure.

The newspaper Ta Nea reported that at least 112 buildings were partially or completely destroyed, with many others cracked and rendered uninhabitable. Twenty percent of Kalamata's building stock, including 44 reinforced concrete structures, was eventually demolished because of the damage. Many displaced residents set up in one of 30 emergency campsites while their neighborhoods were assessed and slowly rebuilt. Some left for Athens and did not return. Reconstruction work lasted five years. In 1987, on the one-year anniversary, Prime Minister Andreas Papandreou did not attend the memorial ceremony, citing his schedule — an absence that became its own kind of minor wound in a city still very much in pain.

The earthquake was not an isolated event but part of a seismically active region with a long memory. The Peloponnese sits above the Hellenic arc, where the African plate subducts beneath the Aegean at a slow but inexorable rate. The region had experienced earthquakes and associated tsunamis before — notably in 1867 and 1947 — and has experienced them since. In the weeks after September 13, aftershocks distributed themselves in two distinct clusters north and south of the main rupture, separated by a quiet zone along the fault where the rupturing had been smooth. At depth, the two clusters merged. The ground continued to adjust for months.