Seismic Swarm PS20190624.1 Near Abepura, Indonesia: Geological Context and Event Analysis

On 24 June 2019, a seismic swarm designated PS20190624.1 was recorded approximately 226 km west of Abepura, Indonesia. The sequence began at 01:05 UTC and concluded at 22:39 UTC, encompassing 13 earthquakes over 21 hours and 34 minutes. Magnitudes ranged from 4.7 to 6.1, with focal depths predominantly between 10 km and 28 km. The events clustered tightly in time, characteristic of swarm activity where no single mainshock dominates the energy release. The sequence opened with a magnitude 6.1 event at 28 km depth, followed rapidly by magnitude 5.0 and 5.1 shocks at 10 km depth. Subsequent activity included multiple events of magnitude 5.0–5.7, with several occurring within minutes of one another in the afternoon hours. Depths remained shallow throughout, consistent with crustal faulting in the region. Such swarms often reflect fluid migration or stress redistribution along interconnected fault segments rather than a classic foreshock-mainshock-aftershock pattern. The Abepura area lies within the tectonically complex zone of western New Guinea, where the Australian and Pacific plates converge. This interaction produces a combination of thrust faulting, strike-slip motion, and localized extension. The broader Papua region experiences frequent moderate-to-large earthquakes due to this ongoing collision, which has shaped the island’s rugged topography and active fault systems over millions of years. Historical records indicate recurrent strong shaking, underscoring the persistent seismic hazard. Notable prior events include a magnitude 7.0 earthquake on 27 July 2015 located 234 km west of Abepura, only 4 km from the 2019 swarm centroid. Another magnitude 7.0 event occurred on 6 April 2013, centered 260 km west-southwest of Abepura and 94 km from the swarm location. These earlier shocks highlight the presence of capable faults capable of generating significant energy release in close proximity to the 2019 sequence. Analysis of the 2019 swarm provides insight into short-term clustering behavior along these structures. The rapid succession of events, all within a compact spatial footprint and limited depth range, suggests activation of a localized fault network under elevated stress conditions. No damage or casualties were widely reported, yet the swarm serves as a reminder of the dynamic nature of seismicity in this plate-boundary setting.

References

USGS Earthquake Catalog
SeismoSight internal swarm classification PS20190624.1