Seismic Swarm PS20010214.1: Analysis of Activity Near Bengkulu, Indonesia

A seismic swarm designated PS20010214.1 occurred approximately 131 km south of Bengkulu, Indonesia, between 19:28 on 13 February 2001 and 04:45 on 14 February 2001. Over 9 hours and 17 minutes, the sequence registered six earthquakes. The events began with a magnitude 7.4 shock at a depth of 36 km, followed by five additional events with magnitudes ranging from 4.7 to 5.6, all at depths of 33 km.

The sequence unfolded as follows: the initial 7.4 event at 19:28:30 on 13 February; a 5.2 event at 22:27:14; another 5.2 at 01:39:31 on 14 February; a 4.7 at 03:08:05; a 5.1 at 03:38:17; and a final 5.6 at 04:45:35. Magnitudes decreased after the mainshock, with most aftershocks clustered at consistent shallow depths indicative of activity within the upper crust.

Bengkulu lies on the western coast of Sumatra within the Sunda subduction zone, where the Indo-Australian Plate converges with the Eurasian Plate at rates of approximately 5–6 cm per year. This tectonic setting produces frequent megathrust earthquakes and associated seismic swarms. The region has a well-documented history of large events, including the magnitude 7.9 earthquake of 4 June 2000 located 103 km south of Bengkulu and the magnitude 7.4 event of 13 February 2001 situated 102 km south-southeast of the city.

Since 1 January 2000, four swarms have been recorded in the area, with three occurring in 2000 and one in 2001. The 2001 swarm centered near the site of the magnitude 7.4 mainshock, suggesting a possible link to post-seismic stress adjustment along the subduction interface or adjacent crustal faults. Depths around 33–36 km align with typical rupture zones in this segment of the Sunda megathrust.

Such swarms contribute to understanding seismic hazard in western Sumatra, where cumulative strain release from moderate sequences can precede or follow great earthquakes. Monitoring these patterns aids in refining models of fault segmentation and recurrence intervals for the Bengkulu segment.

References

USGS Earthquake Catalog (historical event parameters)
SeismoSight internal swarm classification (PS20010214.1 data)