Seismic Swarm Event Near Poso, Indonesia: May 29, 2017

A seismic swarm designated PS20170529.1 occurred approximately 40 km west-northwest of Poso in Central Sulawesi, Indonesia, on May 29, 2017. The sequence began at 14:35 local time and concluded at 15:18, lasting 43 minutes and producing seven earthquakes. Magnitudes ranged from 4.5 to 6.6, with focal depths between 10 and 12 km.

The largest event registered magnitude 6.6 at 14:35:21, followed by events of magnitudes 5.3, 5.1, 4.5, 5.0, 5.1, and 5.0. All subsequent shocks occurred at 10 km depth. This activity represents the second swarm recorded in the region since 2000, following an earlier episode in 2005.

Sulawesi lies at a complex tectonic junction involving the Sunda, Australian, Philippine Sea, and Caroline plates. The island experiences frequent seismicity due to strike-slip faulting along the Palu-Koro Fault System and subduction processes to the east and north. Central Sulawesi, including the Poso area, sits near the boundary where left-lateral shear accommodates regional plate motions.

Historical records document numerous moderate to large earthquakes in Sulawesi, reflecting ongoing deformation. Depths of 10–12 km align with typical upper-crustal events in the region, where brittle failure occurs along active faults. Such swarms often indicate fluid migration or stress transfer along fault segments without producing a single dominant mainshock-aftershock sequence.

No significant damage or casualties were associated with this particular swarm. The event underscores the persistent seismic hazard in Central Sulawesi, where rapid population growth and infrastructure development increase exposure to ground shaking.

References

• USGS Earthquake Catalog (events 2017)
• Tectonic framework of Sulawesi from regional geological surveys
• SeismoSight internal swarm classification data