Seismic Swarm PS20010116.1: Analysis of Activity Southwest of Bengkulu, Indonesia

On 16 January 2001, a seismic swarm designated PS20010116.1 was recorded 92 km southwest of Bengkulu, Indonesia. The sequence began at 13:25 local time and concluded at 16:49, encompassing seven earthquakes over a span of three hours and twenty-four minutes. This event cluster occurred within the tectonically active Sumatran subduction zone, where the Indo-Australian Plate converges with the Eurasian Plate along the Sunda Trench.

The swarm exhibited a range of magnitudes and focal depths. The initial event registered magnitude 6.0 at 33 km depth, followed closely by a magnitude 6.9 shock at 28 km. Subsequent events included magnitudes 5.4, 5.1, 5.2, and 5.6, each at 33 km depth, with a final magnitude 5.7 event at 57 km. Such swarms reflect clustered seismicity often linked to stress adjustments along the subduction interface or associated crustal faults.

Bengkulu Province occupies a position on the southwestern flank of Sumatra, directly above the megathrust boundary. The underlying geology features a complex assemblage of accreted sediments, volcanic arcs, and strike-slip faults such as the Sumatran Fault System, which accommodates oblique convergence. Historical records indicate recurrent large-magnitude events in this corridor, underscoring the region's persistent seismic hazard.

Since 1 January 2000, three swarms have been documented in the vicinity, with the earliest occurring in 2000. Notable strong earthquakes in the same period include a magnitude 7.9 event on 4 June 2000 located 103 km south of Bengkulu and a magnitude 8.4 shock on 12 September 2007 situated 122 km southwest of the city. The 2007 event epicenter lay approximately 34 km from the PS20010116.1 swarm center, highlighting spatial overlap within the same fault segment.

These observations align with the broader tectonic framework of the Sunda megathrust, where episodic slip and afterslip processes can generate both isolated large earthquakes and swarm-type sequences. Continued monitoring of such activity contributes to refined assessments of strain accumulation and rupture potential along this segment of the plate boundary.

References

• SeismoSight internal swarm classification records for PS20010116.1 and associated historical statistics.
• Tectonic summaries of the Sumatran subduction zone from established geophysical literature on Indo-Australian and Eurasian plate interaction.