Seismic History of the Kokopo Region, Papua New Guinea

The M7.6 earthquake that struck 135 km east of Kokopo, Papua New Guinea, on 9 September 2005 at 07:26 UTC originated at a depth of 90 km. This intermediate-depth event reflects the tectonic stresses within the subducting slab beneath the Bismarck Sea. Kokopo lies on the northeastern coast of New Britain Island, where convergence between the Pacific Plate and the Australian Plate produces one of the most seismically active zones on Earth. New Britain occupies a complex plate boundary marked by the New Britain Trench to the north and the Solomon Sea Plate interactions to the south. Subduction of oceanic lithosphere generates frequent earthquakes at depths ranging from shallow crustal levels to more than 200 km. The 90 km focal depth of the 2005 mainshock placed it within the Wadati-Benioff zone, where phase changes and dehydration reactions can trigger large ruptures. Volcanic arcs associated with this subduction, including the active volcanoes near Rabaul caldera, further attest to ongoing plate consumption. Since 2000, the same source region has produced several other great earthquakes, underscoring the persistent seismic hazard. On 16 November 2000, an M7.8 event occurred 135 km southeast of Kokopo. Later that month, an M7.0 earthquake struck 191 km east-southeast of the town. In 2013, an M7.3 quake was recorded 190 km east-northeast of Kokopo. The sequence culminated with an M7.9 event on 17 December 2016 located only 140 km east of Kokopo. These events cluster within roughly 90 km of one another, illustrating the repeated failure of adjacent segments of the subducting slab. Collectively, the 2000–2016 sequence released substantial strain accumulated along the plate interface. Intermediate-depth earthquakes such as these often produce felt shaking across New Britain and adjacent islands, although their depth reduces the likelihood of surface rupture and tsunami generation compared with shallow megathrust events. Regional seismic networks operated by the Papua New Guinea Geological Survey and international agencies continue to monitor aftershock sequences and background seismicity to refine hazard assessments. The tectonic setting of eastern Papua New Guinea remains unchanged, with convergence rates exceeding 10 cm per year. Future large earthquakes are therefore expected. Engineering practices that incorporate the latest ground-motion models and tsunami evacuation planning for low-lying coastal communities around Kokopo remain essential components of disaster risk reduction.

References

USGS Earthquake Catalog (events 2000–2016)
Papua New Guinea Department of Mineral Policy and Geohazards Management seismic reports