Seismic Swarm Near Jayapura, Indonesia: Analysis of Event S20230103.1

A seismic swarm designated S20230103.1 was recorded 15 km east-northeast of Jayapura, Indonesia, beginning at 14:25 on 2 January 2023 and concluding at 15:10 on 5 January 2023. Over the 72-hour-and-45-minute period, 47 earthquakes were detected, with magnitudes ranging from 2.5 to 5.1 and focal depths predominantly between 10 and 28 km.

The sequence exhibited classic swarm characteristics: a gradual increase in event rate without a single dominant mainshock, followed by a decline in activity. The largest events included a magnitude 5.1 earthquake at 12:55 on 3 January (depth 10 km) and another magnitude 5.1 at 12:16 on 4 January (depth 19 km). Earlier notable shocks reached 4.9 on both 3 and 4 January. Depths remained shallow throughout, consistent with crustal deformation in the upper lithosphere.

Jayapura lies within the northern margin of New Guinea, where the Pacific Plate interacts with the Australian Plate along a complex boundary involving both subduction and left-lateral strike-slip motion. The regional tectonics are dominated by the New Guinea Trench system to the north and the Sorong Fault zone, which accommodates oblique convergence. This setting produces frequent moderate earthquakes and occasional swarms driven by fluid migration or stress transfer along fault networks.

Historical records indicate that earthquake swarms are uncommon in this immediate area. Since 1 January 2000, only three such swarms have been identified: two in 2007 and one in 2016. The 2023 event therefore represents a relatively rare episode of clustered seismicity for the Jayapura vicinity.

The swarm’s temporal evolution showed peak activity on 3 January, with 18 events recorded that day, including the sequence’s strongest shocks. Activity tapered steadily on 4 and 5 January, ending with two final magnitude-2.5 events. No damage or casualties were reported, reflecting the moderate magnitudes and offshore-to-coastal location.

Continued monitoring by regional seismic networks remains essential given the persistent tectonic loading in northern Papua. Future swarms in this corridor could provide additional insight into strain accumulation along the plate boundary.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Global CMT Catalog (globalcmt.org)
Geological Survey of Indonesia (pusatgempa.bmkg.go.id)