Seismic Swarm PS20160917.1: Analysis of Activity Near Jayapura, Indonesia

The seismic swarm designated PS20160917.1 occurred approximately 41 km north-northeast of Jayapura, Indonesia, in a tectonically complex region along the northern margin of the island of New Guinea. This area lies at the convergent boundary between the Australian and Pacific plates, where oblique convergence drives a combination of thrust faulting and left-lateral strike-slip motion. The regional geology features the New Guinea Trench to the north and a series of active faults within the Papuan Fold Belt, contributing to elevated seismicity throughout the Cenozoic era.

The swarm initiated at 01:20 on 17 September 2016 and concluded at 07:17 on 18 September 2016, spanning 29 hours and 57 minutes. Six earthquakes were recorded during this interval, with magnitudes ranging from 4.3 to 6.0 and focal depths between 9 and 12 km. The sequence began with a magnitude 6.0 event at 9 km depth, followed by a magnitude 5.2 shock roughly 46 minutes later. Subsequent events included magnitudes 5.1, 5.0, 4.3, and a final magnitude 5.8 event on 18 September. Depths remained consistently shallow, consistent with activity on upper-crustal structures.

Earthquake swarms differ from typical mainshock-aftershock sequences by lacking a single dominant event and instead featuring comparable magnitudes distributed over time. In this case, the temporal clustering and similar depths suggest possible involvement of fluid migration or stress transfer along interconnected fault segments within the plate-boundary zone. Such swarms are documented in other convergent margins and can indicate transient changes in pore pressure or aseismic slip.

Historical records maintained since 1 January 2000 indicate that only three swarms have occurred in this vicinity, with the earliest documented in 2007. This low frequency underscores the episodic nature of swarm activity compared with the more continuous background seismicity driven by ongoing plate convergence at rates of approximately 10–12 cm per year.

The shallow depths of the PS20160917.1 events imply potential for felt shaking in Jayapura and surrounding coastal communities, although no damage reports are associated with this particular swarm. Continued monitoring remains essential given the region’s history of larger thrust earthquakes capable of generating tsunamis.

References

SeismoSight internal swarm catalog
USGS Earthquake Hazards Program regional tectonics summary
Global CMT moment tensor database for Papua New Guinea events