Location:

Period:

27 Jun 2008 11:40:13 - 29 Jun 2008 04:14:37 (1 day 16 hours 34 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

4 swarms found nearby.

2004

PS20041226.11(84.6km)

26 Dec

13 hours

5 earthquakes

PS20041226.4(124.4km)

26 Dec

2 days 11 hours

14 earthquakes

2005

PS20050104.1(17.1km)

4 Jan

10 hours

5 earthquakes

2008

PS20080810.1(7.1km)

10 Aug

5 hours

5 earthquakes

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Seismic Swarm PS20080627.1: Activity Southwest of Port Blair

An earthquake swarm designated PS20080627.1 occurred 127 km southwest of Port Blair in the Andaman Sea, India. The sequence began at 11:40 on 27 June 2008 and concluded at 04:14 on 29 June 2008, spanning 40 hours and 34 minutes. During this interval, ten earthquakes were recorded, with magnitudes ranging from 5.0 to 6.6 and focal depths between 10 and 29 km.

The swarm initiated with a magnitude 6.6 event at 17 km depth on 27 June at 11:40. Subsequent events included a magnitude 5.9 at 13:07 and a magnitude 5.2 at 13:10, both at shallow depths. Later that day, a magnitude 5.0 event occurred at 25 km depth. On 28 June, activity continued with a magnitude 5.1 at 29 km, followed by a magnitude 6.1 at 15 km depth. Additional events reached magnitudes 5.4, 5.0, and 5.2 at depths of 20–24 km. The final recorded earthquake was a magnitude 5.2 at 23 km depth on 29 June.

This region forms part of the Sunda subduction zone, where the Indian Plate converges with the Burma Plate at rates of approximately 5–6 cm per year. The oblique subduction generates thrust faulting and strike-slip motion along the Andaman Trench, producing frequent seismic sequences. Depths recorded in the swarm align with the shallow megathrust interface and overlying crustal faults typical of this tectonic setting.

The Andaman-Nicobar Islands have experienced significant historical seismicity. The 26 December 2004 Sumatra-Andaman earthquake of magnitude 9.1–9.3 ruptured a 1,600 km segment of the plate boundary, generating widespread aftershock sequences that persisted for years. Post-2004 activity included multiple clusters in the Andaman Sea, consistent with stress redistribution along the subduction interface.

Since 2000, three swarms have been identified in the area under SeismoSight classification, occurring in 2004 (two events), 2005 (one event), and the 2008 sequence detailed here. Such swarms often reflect fluid migration or aseismic slip triggering brittle failure at multiple depths.

The 2008 swarm’s temporal clustering and magnitude distribution illustrate typical behavior along this convergent margin, where moderate events can occur without a single dominant mainshock.

References USGS Earthquake Catalog (earthquake.usgs.gov) Global CMT Catalog (globalcmt.org) Indian Meteorological Department Seismology Division reports