Seismic Swarm Activity in the Kepulauan Mentawai Region, Indonesia

A seismic swarm designated PS20230422.1 was recorded in the Kepulauan Mentawai region of Indonesia on 22 April 2023. The sequence began at 17:09 and concluded at 23:33, spanning 6 hours and 24 minutes, during which five earthquakes occurred. The events ranged in magnitude from 4.7 to 5.8 and originated at depths between 16 and 22 km. Specific timings include a magnitude 5.8 event at 17:09:44, followed by a 5.7 at 21:17:47, a 5.2 at 21:20:55, a 4.7 at 23:11:15, and a final 5.2 at 23:33:52.

Such swarms represent clustered seismic activity without a dominant mainshock, often linked to fluid migration or stress redistribution along fault interfaces in subduction settings. In the Mentawai area, they may reflect adjustments within the accretionary wedge or upper plate structures above the Sunda megathrust.

The Kepulauan Mentawai lie above 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 regime has produced recurrent large earthquakes and associated tsunamis throughout the Holocene. Historical records document major events, including the 1797 and 1833 earthquakes that generated significant tsunamis impacting the islands and adjacent Sumatran coast. More recently, the 2004 Indian Ocean earthquake and the 2010 Mentawai event underscore the persistent seismic hazard.

Since 2000, four prior swarms have been identified in the region during 2005, 2007, 2009, and 2018. These episodes illustrate episodic clustering that supplements the background rate of isolated events. On 24 April 2023, a magnitude 7.1 earthquake occurred 171 km south-southeast of Teluk Dalam, approximately 7 km from the swarm centroid, highlighting continued tectonic activity shortly after the swarm.

Ongoing monitoring by regional networks contributes to refined understanding of strain accumulation and release patterns along this portion of the megathrust. Such data support probabilistic seismic hazard assessments for coastal communities in western Sumatra and the Mentawai Islands.

References
USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
SeismoSight internal swarm classification records