1981 Gulf of Corinth earthquakes
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  24 Feb 25 Feb 4 March  Athens | |
| UTC time | |
|---|---|
| A: 1981-02-24 20:53:38 | |
| B: 1981-02-25 02:35:53 | |
| C: 1981-03-04 21:58:05 | |
| ISC event | |
| A: 631767 | |
| B: 631819 | |
| C: 629205 | |
| USGS-ANSS | |
| A: ComCat | |
| B: ComCat | |
| C: ComCat | |
| Local date | |
| A: 24 February 1981 | |
| B: 25 February 1981 | |
| C: 4 March 1981 | |
| Magnitude | |
| A: 6.7 Ms | |
| B: 6.4 Ms | |
| C: 6.4 Ms | |
| Depth | |
| A: 33.0 km | |
| B: 33.0 km | |
| C: 28.5 km | |
| Epicentre | 38°13′19″N 22°56′02″E / 38.222°N 22.934°E |
| Type | Normal |
| Areas affected | Greece, Gulf of Corinth, Athens |
| Total damage | $812 million[1] |
| Max. intensity | MMI IX (Violent) |
| Tsunami | minor |
| Casualties | 22 dead, 400 injured |
In early 1981 the eastern part of the Gulf of Corinth in Greece was struck by three earthquakes with a magnitude greater than 6 Ms over a period of 11 days. The earthquake sequence caused widespread damage in the Corinth–Athens area, destroying nearly 8,000 houses and causing 20–22 deaths.
The Gulf of Corinth is an area of active extensional tectonics. The underlying cause of this extension has been attributed to rollback of the African plate as it subducts northwards beneath the Aegean Plate. Other possible mechanisms include gravitational collapse of crust overthickened during the Paleogene to early Neogene or the effects of the continuing propagation of the North Anatolian Fault towards the southwest.[2]
The rift that formed the Gulf of Corinth is bounded by large normal faults that vary in their polarity (dip direction) along its length. The eastern end of the rift, which forms the Alkyonides Gulf, is dominated by north-dipping faults, including the Perachora, Straya, Skinos, Pisia, West Alkyonides and East Alkyonides faults. Immediately to the east, the large south-dipping Kaparelli Fault forms the northern boundary to the onshore continuation of the rift zone.[2]
Earthquake sequence
The first earthquake in the sequence occurred at 20:53 UTC on 24 February. It had a magnitude of 6.7 Ms and a maximum felt intensity of IX (violent) on the Modified Mercalli intensity scale (MMI).[3] The epicentre was at the western end of the Alkyonides Gulf and involved rupture of the Pisia Fault and possibly the Skinos Fault. The assignment of the observed surface ruptures to the first two earthquakes in the sequence remains uncertain as they occurred over the same night. The maximum measured offset on the Pisia Fault was 150 cm, while that on the Skinos Fault was 100 cm.[4]
The second earthquake occurred less than 6 hours later at 02:35 UTC on 25 February, with a magnitude of 6.4 Ms , also with a maximum felt intensity of IX (MMI).[5] The epicentre was in the central part of the Alkyonides Gulf and involved the rupture of the Skinos Fault and possibly the Pisia Fault.[4]
The final earthquake in the sequence occurred over ten days later at 21:58 UTC on 4 March, also with a magnitude of 6.4 Ms and a maximum felt intensity of IX (MMI).[6] The epicentre was just to the east of the Alkyonides Gulf and involved the rupture of the Kaparelli Fault, with a maximum observed displacement of 100 cm.[4]
Analysis of stress changes associated with the February 24 earthquake show increases on the fault segments that ruptured during the other two events.[7]