Location:

Period:

2 Sep 2009 08:17:36 - 7 Sep 2009 12:30:21 (5 days 4 hours 12 minutes)

Volcanoes in 100km radius:

Methana(51km)

Earthquakes:

3 swarms found nearby.

2011

S20110127.2(18.8km)

27 Jan

22 hours

44 earthquakes

2021

S20210711.1(27.8km)

10 Jul

2 days 10 hours

58 earthquakes

S20210720.2(27.1km)

20 Jul

1 day 23 hours

38 earthquakes

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Seismic Swarm S20090902.1: Insights into Greece's Tectonic Activity

Seismic swarms represent clusters of earthquakes occurring in a localized area over a short period without a dominant mainshock. Swarm S20090902.1, recorded in Greece, began at 08:17 on 2 September 2009 and concluded at 12:30 on 7 September 2009. Over 124 hours and 12 minutes, the event registered 95 earthquakes, with magnitudes ranging from 1.4 to 4.4 and focal depths predominantly between 3 and 30 km.

The temporal distribution showed peak activity on the first day, including the largest event of magnitude 4.4 at a depth of 4 km. Subsequent days featured numerous events between magnitudes 2.0 and 3.2, with depths clustering around 5–15 km. This pattern aligns with fluid-driven or stress-transfer mechanisms typical of swarms in extensional or subduction-related settings, where small-magnitude events occur in rapid succession.

Greece lies at the convergent boundary between the African and Eurasian plates along the Hellenic Arc. The region experiences oblique subduction, back-arc extension in the Aegean, and strike-slip faulting, resulting in one of Europe's highest seismic hazard levels. Shallow crustal seismicity, as observed in this swarm, commonly arises from normal faulting within the overriding plate or volcanic processes in areas such as the South Aegean.

Historical records document recurrent seismic swarms in Greece, particularly in the Corinth Gulf, Ionian Islands, and volcanic centers like Santorini. These episodes often precede or accompany larger tectonic events, reflecting ongoing plate convergence at rates of 35–40 mm per year. Updated monitoring by national networks confirms continued microseismicity across these zones, underscoring the persistent geodynamic forces.

Analysis of depth and magnitude trends in S20090902.1 indicates predominantly shallow sources, consistent with brittle failure in the upper crust. Such swarms contribute valuable data for refining seismic hazard models, as they highlight zones of elevated strain accumulation without producing destructive shaking.

References

Hellenic Seismic Network bulletins (Institute of Geodynamics, National Observatory of Athens)
USGS Earthquake Catalog for regional tectonics
McKenzie, D. (1978). Active tectonics of the Alpine–Himalayan belt. Geophysical Journal International.