1986 Kalamata earthquake

1986 Kalamata earthquake
1986 Kalamata earthquake is located in Greece
1986 Kalamata earthquake
UTC time1986-09-13 17:24:31
ISC event486403
USGS-ANSSComCat
Local date13 September 1986 (1986-09-13)
Local time20:24 EET
Magnitude6.0 Mw
6.2 Ms
Depth11.2 km (7.0 mi)
Epicenter37°00′50″N 22°10′34″E / 37.014°N 22.176°E / 37.014; 22.176Coordinates: 37°00′50″N 22°10′34″E / 37.014°N 22.176°E / 37.014; 22.176
TypeNormal
Areas affectedGreece
Max. intensityX (Extreme)
TsunamiNone
Casualties20–24 dead, 300 injured

The 1986 Kalamata earthquake struck the southern Peloponnese Region of Greece on September 13 at 20:24 local time. The moment magnitude 6.0 or surface-wave magnitude 6.2 earthquake had an epicenter located near the coastal city of Kalamata. It was assigned X (Extreme) on the Modified Mercalli intensity scale caused by extensive damage in Kalamata. At least 20 people died and approximately 300 were injured.

Tectonic setting

Greece is a seismically active country, located in a complex zone of interaction of the African, Eurasian, Aegean Sea, and Anatolian Plates. Southern Greece itself is located on the Aegean Sea Plate. The Anatolian Plate is moving southwest into the Aegean Sea Plate at a rate of 3 cm per year relative to the Eurasian Plate. Meanwhile, the African Plate undergoes subduction beneath the Aegean Sea Plate at a rate of 4 cm per year along the Hellenic subduction zone.

The earthquake occurred in a region of the Aegean Sea characterized by active extensional tectonics which has been ongoing since the Pliocene. Extension is uniform in the central area and most of the Aegean Sea; in a north-south direction. Just north of the Hellenic trench; the southern Aegean Sea however, extension is complex, occurring in both a north-south and east-west direction.

Earthquake

According to the National Observatory of Athens, the earthquake registered ML 5.5 on the Richter scale. It measured much higher on the surface-wave and moment magnitude scales at Ms  6.2 and Mw  6.0, respectively.

Characteristics

The city of Kalamata is located at the borders of the valley of Messinia and the Messenian Gulf, which forms a graben feature. To the east are the Taygetus mountain range, which is separated from the graben by a series of normal dip-slip faults, which are part of the seismic zone of Western Mani. These faults generally trend north-south, causing east-west extension. One of them is the Kalamata Fault, which runs in a northwesterly direction. This region of Southern Greece is no stranger to earthquakes and their associated tsunamis, including an 1867 event that caused a tsunami and another 1947 earthquake.

An analysis of the earthquake focal mechanism corresponds to shallow normal faulting at a shallow depth of 8 km to 11.2 km. The rupture zone of the event was determined to be on a 15 km-long by 10-km-wide fault known as the Kalamata Fault, based on inferring the distribution of aftershocks. The fault ruptured to the surface along its northern extent, causing surface ruptures. The Kalamata Fault is part of a group of faults that separates the Taygetus mountains from the Pamisos river plain.

Surface rupture

Small but distinct normal fault scarps and surface ruptures were observed for a total length of 6 km, with some interruptions. Seismologists were able to trace a strand of surface rupture for a length of 4.5 km. Surface ruptures were sometimes accompanied by a fissure. Some surface ruptures measured up to 6–18 cm in vertical height, and were as wide as 2–6 cm. These surface ruptures often appeared in terraced olive groves near rocky outcrops. The surface ruptures were several tens of centimeters west of a large fault surface (slickenside). The fault is responsible for uplift of the Taygetus mountains.

Intensity

The greater Kalamata and Elaiochori regions were within the meizoseismal area, where the seismic intensity peaked at X (Extreme). The city center experienced intensity VIII (Severe), where heavy damage was reported in Kalamata; 42% of homes were obliterated or damaged to the extent that they were irrepairable. In Elaiochori and Perivolakia, the intensity was X and the towns were completely destroyed. A study of the earthquake's effects at Elaiochori, a village located 525 meters on a mountain found that strong ground motions were greatly amplified. Seismic waves had short periods of 0.15–1.6 seconds, affecting short, poorly built structures. The high-frequency seismic energy in Elaiochori meant that structures were unable to withstand intense shaking. Intensity VIII was felt in Verga and Poliani. In Aris, Artemisia, and Nedousa, the intensity was VII (Very strong). Nedousa suffered serious damage as well. Intensity VI (Strong) was felt in Achladochori, Chelidoni, Ampheia and Kampos. Weaker shaking V (Moderate) was assigned in Andritsaina-Krestena, Goumero, and Makrisia.

Aftershocks

More than 700 aftershocks were recorded in the first two weeks after the mainshock. The aftershocks were located in two distinct clusters, the north and south, separated by a gap. The aftershocks focal depths were up to 10 km deep. The southern sequence initiated right after the mainshock at the southern extension of the fault, releasing strain that still remained after the mainshock. The northern aftershock swarm was more active and located further from the surface ruptures, between the Kalamata Fault and the Thuria Fault.

On the 15th of September, a Ms  5.3 aftershock occurred south of the mainshock with a Mercalli intensity of VI (Strong), causing 37 injuries and further damage in the Kalamata area.

Impact

Damage sustained by the Metropolitan Church of Ypapantis after the earthquake and its subsequent aftershocks.
A USGS ShakeMap of the earthquake.

The high intensity brought by the earthquake resulted in very heavy structural damage. Initial reports said that 112 homes constructed of stone were destroyed and a further 1,100 were damaged. In Kalamata, where shaking intensity was reported at VIII (Severe), the earthquake razed four buildings to the ground. At least 20% of all structures in the city were so badly damaged that they were unsafe for use, and were demolished. A further 16% of buildings suffered more serious damage, and in the other 36%, damage was moderate. The western part of Kalamata, despite being close to the epicenter, suffered less severe damage.

The effects of the quake on other types of man-made structures, such as bridges and industrial facilities, however, suffered very little damage, or were practically unaffected. The only structural damage was at the jetty at Kalamata, where cracks up to 10 cm wide were reported. In some locations, the jetty walls partially detached. The quake also caused power outages and disrupted communication services in the city.

The Metropolitan church of Ypapanti suffered severe damage as a result of the earthquake, and had to be restored. It was the second time the church had been damaged by an earthquake, the previous one during the 1886 Peloponnese earthquake. Another church, the Church of Agioi Apostoloi experienced a partial collapse in the quake when its dome and roof fell. It was the first time the church had sustained earthquake damage since 1884. The collapse of the defensive towers of the Holy Monastery of Velanidia (gr) claimed the lives of three individuals.

At Elaiochori, located 7 km from Kalamata, the quake destroyed at least 70% of the buildings. Only 120 buildings were left intact by the end of the quake. The town suffered tremendous damage because it was located in the meizoseismal area, where maximum intensity X (Extreme) was assigned on the Mercalli intensity scale. There were also additional reports of extreme damage in the villages Verga, Poliani, Aris, Artemisia and Nedousa.

Some rockfalls were reported in the Taygetus mountains, and some blocked a major road that linked Kalamata to the town of Sparta, Laconia.

Total damage caused by the earthquake has been estimated to be €670,000,000 Euros.

Casualties

The quake killed at least 20 people. Of those, six bodies were recovered from a five story reinforced concrete apartment tower that collapsed in the mainshock. Another 15 people were rescued from the same apartment structure after many hours of efforts. Four people died when an old stone building collapsed in Elaiochori, Messenia. Six people were killed by falling roadside debris. Of the six, one person was crushed by a roof, one by a heart attack, one infant by suffocation and one person by severe injuries. In addition, 330 people were injured, 83 of them has injuries so serious that immediate medical attention was required.

Despite the severity of damage however, the death toll was low because most residents were attending a ferry line opening ceremony when the earthquake occurred.

See also


This page was last updated at 2022-09-14 11:16 UTC. Update now. View original page.

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