Location:

Period:

30 Mar 2009 13:38:39 - 7 Jul 2009 05:49:39 (98 days 16 hours 11 minutes)

Volcanoes in 100km radius:

Colli Albani(86km)

Earthquakes:

6163

19 swarms found nearby.

2009

S20090407.1(14.2km)

6 Apr

14 days 13 hours

720 earthquakes

S20090409.1(15.4km)

8 Apr

3 days 2 hours

130 earthquakes

S20090412.1(18.2km)

11 Apr

8 days 23 hours

375 earthquakes

S20090421.1(17.0km)

20 Apr

20 days 8 hours

436 earthquakes

S20090429.1(14.3km)

28 Apr

1 day 20 hours

28 earthquakes

S20090501.1(15.0km)

30 Apr

1 day 9 hours

26 earthquakes

S20090510.1(17.1km)

9 May

13 days 16 hours

178 earthquakes

S20090626.1(26.8km)

25 Jun

3 days 7 hours

118 earthquakes

S20090629.1(16.6km)

28 Jun

9 days 0 hours

138 earthquakes

S20090704.2(15.9km)

3 Jul

14 days 1 hours

237 earthquakes

S20090713.1(25.4km)

12 Jul

6 days 5 hours

128 earthquakes

S20090801.1(11.8km)

31 Jul

19 days 15 hours

224 earthquakes

S20090823.1(28.5km)

22 Aug

6 days 9 hours

83 earthquakes

2010

S20100831.1(25.1km)

30 Aug

25 days 22 hours

427 earthquakes

S20101001.1(26.2km)

30 Sep

11 days 3 hours

111 earthquakes

S20101104.1(26.6km)

3 Nov

6 days 0 hours

176 earthquakes

2011

S20110215.1(5.4km)

15 Feb

1 day 8 hours

27 earthquakes

S20110306.1(26.5km)

5 Mar

8 days 1 hours

87 earthquakes

2017

S20170118.1(24.5km)

18 Jan

5 days 9 hours

231 earthquakes

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Seismic Swarm S20090330.1: Foreshock Sequence in Central Italy

Central Italy lies within the Apennine mountain chain, where ongoing extensional tectonics driven by the rollback of the Adriatic slab produces frequent seismic activity. The region features active normal faults oriented northwest-southeast, capable of generating moderate to strong earthquakes at shallow depths. Historical records document destructive events such as the 1703 Norcia earthquake and the 1915 Avezzano earthquake, both linked to the same fault systems.

Swarm S20090330.1 began at 13:38 on 30 March 2009 and continued until 05:49 on 7 July 2009, registering 6163 earthquakes over 2368 hours. The sequence occurred in the L’Aquila area of the Abruzzo region. Analysis of the first 100 events reveals predominantly low-magnitude activity clustered at shallow crustal depths. The initial event reached magnitude 4.3 at 5 km depth, followed by numerous events between magnitude 1.5 and 2.5. Depths averaged near 10 km, with occasional shallower or deeper occurrences up to 15 km.

Larger foreshocks included magnitudes 3.8, 3.9, 3.5, 4.0 and several events above 3.0, distributed across the first five days. Magnitudes remained mostly below 3.0 after the opening hours, indicating a typical swarm pattern of sustained microseismicity punctuated by occasional moderate shocks. The sequence intensified in early April, culminating in the 6 April 2009 L’Aquila mainshock of magnitude 6.3.

This foreshock activity highlighted the progressive failure along the Paganica fault. The spatial concentration and temporal evolution of the initial 100 events provided early indications of strain accumulation within the central Apennines extensional regime. Depths consistently in the upper 15 km align with the brittle-ductile transition zone characteristic of the region’s continental crust.

Post-swarm studies have refined understanding of fluid involvement and fault interactions in triggering prolonged sequences. The 2009 activity remains a key case study for seismic hazard assessment in the Apennines, underscoring the value of dense monitoring networks for early detection of foreshock patterns.

References

SeismoSight internal swarm classification S20090330.1
INGV seismic catalogue (updated 2023)
USGS Earthquake Hazards Program
Journal of Geophysical Research: Solid Earth (2009–2010 L’Aquila sequence papers)