Seismic Swarm PS20191022.1: Analysis of Earthquake Activity West of Abepura, Indonesia

A seismic swarm designated PS20191022.1 occurred approximately 252 km west of Abepura, Indonesia, beginning at 19:15 on 22 October 2019 and concluding at 05:56 on 23 October 2019. Over the 10-hour-and-41-minute period, nine earthquakes were recorded. All events were shallow, with focal depths ranging from 10 km to 24 km, consistent with activity along regional fault structures in a tectonically complex zone.

The sequence began with a magnitude 5.5 event at 19:15:28 on 22 October, followed by a magnitude 5.2 shock nine minutes later. Subsequent events included magnitudes 4.3, 5.1, 5.0, and another 5.1 at depths of 10–21 km through the evening of 22 October. Early on 23 October, magnitudes of 5.0, 5.4, and a final 5.0 at 24 km depth completed the swarm. These closely spaced occurrences without a single dominant mainshock illustrate typical swarm behavior, where energy release is distributed across multiple events of similar size.

Regional Geological Context

The swarm location lies within the western Papuan region of Indonesia, part of the collision zone between the Australian and Pacific plates. This area features oblique convergence accommodated by the New Guinea Trench and associated strike-slip faults. Crustal deformation produces frequent shallow seismicity, with the overriding plate exhibiting fragmented blocks that facilitate swarm-type sequences. Depths of 10–24 km align with the brittle upper crust where such fault interactions commonly occur.

Historical Seismicity

Since 1 January 2000, three swarms have been documented in the vicinity, including one event in 2011 and two in 2019. A notable strong earthquake of magnitude 7.0 struck on 27 July 2015 at a site 234 km west of Abepura, approximately 26 km from the 2019 swarm center. This event underscores the potential for larger-magnitude activity along the same structural trends.

The October 2019 swarm adds to the record of distributed, moderate-magnitude sequences that characterize the region’s seismic regime. Such patterns reflect ongoing plate-boundary strain accumulation rather than isolated mainshock-aftershock sequences.

References

• SeismoSight internal swarm classification data (PS20191022.1 parameters and historical swarm counts)
• Regional tectonic framework derived from standard geological surveys of the New Guinea collision zone