1986 Kalamata Earthquake

The 1986 Kalamata earthquake struck the southern Peloponnese Region of Greece on September 13 at 20:24 local time. The deep moment magnitude () 5.9 earthquake had an epicenter near the coastal city of Kalamata and was assigned X (''Extreme'') on the Mercalli intensity scale. The earthquake was the result of normal faulting along a northwest-dipping fault and produced surface ruptures. Extensive damage was reported in Kalamata and Elaiochori. At least 20 people died and 330 were injured. Survivors sought refuge at campsites and reconstruction work lasted five years.

Tectonic setting

Greece is a seismically active country located in a complex zone of interaction between the African plate the Aegean Sea. Along the Hellenic arc, the African plate subducts beneath the Aegean Sea at around per year. Shallow-focus earthquakes of less than depth are common—the result of accommodating convergence via subduction-related deformation. Back-arc extension occurs within the Aegean Sea, above the subducting crust, causing normal and strike-slip faulting earthquakes. Large intermediate-depth earthquakes occur due to deformation within the subducting plate. The Peloponnese region is characterized by active extensional tectonics which has continued since the Pliocene and the Messenian Gulf which forms a graben. To the east is the Taygetus mountain range; separating it from the graben is a series of normal dip-slip faults, which are part of a seismic zone in West Mani. These faults generally trend north–south and accommodates east–west extension. One of them is the Kalamata Fault which strikes north northeast–south southwest and dips northwest at 70–80°. The Kalamata Fault is part of a group of west-dipping faults that separates the Taygetus mountains from the Pamisos river plain. Believed to have formed during the Quaternary, it was not associated with any earthquakes or surface ruptures prior to 1986. The region frequently experience earthquakes and their associated tsunamis and liquefaction such as in 1867 and 1947.

Earthquake

The earthquake, with a moment magnitude of 5.9, originated at a depth of . The timing of occurrence was at 20:24 EET on 13 September. It was caused by normal faulting along a north-northeast–south-southwest striking and west–northwest dipping fault. The causative fault was later known as the Kalamata Fault; the rupture of the fault occurred across an area estimated at . The fault ruptured to the surface along its northern extent, causing surface ruptures.

Surface rupture

Small fault scarps and surface ruptures were observed east of Kalamata and aligned with a known fault. These were reported for along a north-northeast–south-southwest trend, and were intermittently accompanied by a fissure. One of these ruptures was mapped continuously for . Some ruptures measured up to in vertical height and were wide. They often appeared in terraced olive groves near rocky outcrops, and were several tens of centimeters west of a large fault surface. Heavy damage occurred in homes where the surface rupture propagated beneath.

The most significant surface rupture occurred within an existing north-northeast trending fault trace in the Mesozoic limestone in Elaiochori and Perivolakia. It exhibited a vertical displacement of on the northwest side of the fault, horizontal heave of , and left-lateral offset of . The occurrence of unconsolidated breccia suggest the same fault has reactivated in past earthquakes.

Strong ground motion

Two accelerographs in Kalamata recorded a maximum peak ground acceleration (pga) of 0.27 ''g'' in the horizontal component. Meanwhile, the pga in the veritcal component was 0.368 ''g''. Ground motion in excess of 0.1 ''g'' lasted for 2.5 seconds while the maximum horizontal velocity was per second. The greater Kalamata and Elaiochori regions were within the meizoseismal area.

Downtown Kalamata experienced Modified Mercalli intensity VIII (''Severe''), where damage was heavy; 42 percent of homes were obliterated or had irreparable damage. However, In Elaiochori and Perivolakia, the Modified Mercalli intensity was X (''Extreme'') and both villages were razed. The earthquake produced seismic waves with a short period of 0.15–1.6 seconds, affecting short and poorly built structures. Buildings in Elaiochori were poorly constructed and without retrofitting, could not endure the shaking.

Aftershocks

Following the mainshock, seismic instruments were installed by the National Observatory of Athens, University of Athens, Institut de Physique du Globe de Paris and Grenoble Observatory. These instruments allowed scientists to determine the focal mechanism and depth of aftershocks. About 740 aftershocks were recorded in the first two weeks after the mainshock. Most aftershocks had focal mechanisms consistent with the mainshock (normal) while some were dextral strike-slip events on a fault perpendicular to the mainshock source. The largest aftershock on 15 September measured 5.3 and occurred south of the mainshock. It had a maximum intensity of VII (''Very strong''), caused 37 injuries, and further damage in Kalamata.

These aftershocks were distributed across a × zone in two distinct clusters; north and south, separated by a zone without any. The gap measured and extended to a depth of . The lack of seismicity in the gap was the result of smooth rupturing along the fault. At depth, the two aftershocks clusters merged. These aftershocks had focal depths up to deep but none originated beyond . The southern sequence initiated immediately following the mainshock at the southern extension of the Kalamata Fault, releasing strain that still remained. The northern aftershock swarm experienced greater activity.

Impact

The earthquake caused million in damage. At least 20 people died; more deaths were prevented because most residents attended a ferry line opening ceremony when the earthquake occurred. Six bodies were recovered from a five-story reinforced concrete apartment that collapsed. Six people died from falling debris; one person was crushed, one died from a heart attack, an infant died from suffocation and another from serious injuries. Three individuals perished when the Holy Monastery of Velanidia's defensive towers collapsed. Four people died when an old stone building collapsed in Elaiochori. An additional 330 people were injured including 83 with serious injuries.

The damage in Kalamata mainly occurred in the historic district, in the city's central and northeast corners. There, most buildings were constructed with masonry, and were about 150 to 200 years old. According to '' Ta Nea'', at least 112 buildings were partially or completely destroyed while many others were cracked. Twenty percent of the city's buildings, including 44 reinforced concrete structures, were demolished due to the extent of damage. At a jetty, cracks up to wide were reported and parts of its walls partially detached. Power outages occurred and communication services were disrupted in the city. Some rockfalls occurred in the Taygetus mountains, obstructing a major road that linked Kalamata to Sparta.

Other structures such as bridges and industrial facilities sustained little damage or were unaffected. At Elaiochori, located from Kalamata, at least 70 percent of its buildings were destroyed, leaving only 120 intact. Heavy damage also occurred in the villages of Verga, Poliani, Aris, Artemisia and Nedousa.

Aftermath

Rescuers immediately attended to two buildings in Kalamata; a collapsed apartment and another two-storey house where two people were trapped. They were accompanied by members of the Greek Army, Police and Fire Service. Rescuers pulled four survivors from the apartment building immediately. Another seven people were rescued the following afternoon. Rescue efforts were disrupted by curious onlookers, friends and family members of those trapped visiting the site. Rescue teams from France and Germany also assisted. Many displaced individuals sought refuge across 30 campsites while their homes were reconstructed and some left the city for other areas such as Athens.

In 1987, Prime Minister Andreas Papandreou did not attend a memorial ceremony on the one-year anniversary of the earthquake, citing his busy schedule. Instead, he boarded a cruise with Dimitra Liani which sparked anger among the public.

See also

* List of earthquakes in 1986
* List of earthquakes in Greece

References

Sources

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Further reading

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{{Portal bar, Earth sciences, Greece

1986 earthquakes
Earthquakes in Greece
1986 in Greece
Kalamata
History of Messenia
Geography of Messenia
1986 disasters in Greece
Andreas Papandreou