Location:

Period:

17 Nov 2015 07:10:07 - 1 Dec 2015 13:33:20 (14 days 6 hours 23 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

394

9 swarms found nearby.

2003

PS20030814.1(53.7km)

14 Aug

11 hours

5 earthquakes

S20030814.1(26.8km)

14 Aug

4 days 19 hours

105 earthquakes

2007

S20070325.1(18.0km)

25 Mar

17 days 7 hours

255 earthquakes

S20070418.1(27.8km)

17 Apr

9 days 0 hours

85 earthquakes

S20070502.1(19.4km)

1 May

11 days 4 hours

139 earthquakes

2014

S20140127.2(14.2km)

26 Jan

9 days 1 hours

185 earthquakes

2015

S20151129.1(28.4km)

28 Nov

3 days 13 hours

53 earthquakes

2018

PS20181026.1(110.1km)

25 Oct

14 hours

8 earthquakes

2024

S20240303.2(13.6km)

2 Mar

5 days 9 hours

236 earthquakes

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Seismic Swarm S20151117.1: Analysis of Greece's 2015 Seismic Episode

Seismic swarm S20151117.1 occurred in Greece from 07:10 on 17 November 2015 to 13:33 on 1 December 2015. Over 342 hours and 23 minutes, 394 earthquakes were recorded. Analysis of the first 100 events reveals a classic aftershock sequence initiated by a magnitude 6.5 mainshock at 11 km depth. Subsequent events showed a rapid decline in magnitude, with the majority falling between 2.0 and 4.4 and depths concentrated between 1 km and 22 km.

The initial event at 07:10:07 was followed within minutes by a magnitude 4.0 shock at 4 km depth. Early activity included multiple events above magnitude 3.0, such as a magnitude 5.1 earthquake at 9 km depth roughly 83 minutes after the mainshock. Magnitudes progressively decreased, with events clustering around 2.2–3.4 in the hours that followed. Depths remained predominantly shallow, consistent with upper-crustal faulting. Notable later events within the first 100 included a magnitude 4.3 at 11 km and several magnitude 4.2 shocks at depths of 7–10 km.

This pattern indicates stress redistribution along a fault system after the primary rupture, with aftershocks filling areas of increased Coulomb stress. The swarm's shallow focus suggests activation of brittle crust typical of the Aegean region. No events exceeded the initial magnitude 6.5, confirming the sequence as a mainshock-aftershock series rather than a progressive swarm.

Greece lies at the convergent boundary between the African and Eurasian plates, where the African plate subducts beneath the Aegean plate along the Hellenic Arc. This tectonic setting produces frequent moderate-to-large earthquakes and occasional swarms. The Hellenic subduction zone, combined with strike-slip faulting in the Aegean, accounts for the region's high seismicity. Historical records document destructive events throughout antiquity and the modern era, including the 365 CE Crete earthquake and the 1999 Athens quake.

Since 1 January 2000, Greece has experienced six seismic swarms according to SeismoSight internal classification. Prior episodes occurred in 2003 (two swarms), 2007 (three swarms), and 2014 (one swarm). These recurrent swarms highlight episodic stress release along secondary faults rather than continuous background seismicity.

The 2015 swarm's characteristics align with known Aegean tectonics, where shallow crustal earthquakes dominate. Depths mostly under 15 km reflect the brittle-ductile transition in this extensional back-arc environment. Continued monitoring remains essential given Greece's exposure to seismic hazards.

References

Hellenic Arc tectonics: USGS Earthquake Hazards Program
Aegean seismicity overview: European-Mediterranean Seismological Centre (EMSC) annual reports
Greek historical earthquake catalogue: National Observatory of Athens (NOA) database