by Paul Somerville, Risk Frontiers.
The December 17, 2016, M 7.9 earthquake originated about 46 km east of Taron, New Ireland, Papua New Guinea at a depth of 103 km (Figure 1). It occurred as the result of reverse faulting at an intermediate depth. At the location of the earthquake, the Australia plate converges with and subducts beneath the Pacific plate at a rate of about 105 mm/yr towards the east-northeast. The earthquake occurred within the interior of the subducted Australia plate lithosphere, rather than on the shallow thrust interface between these two plates. The detailed slip map and time function of the earthquake show that it had a source duration of 80 seconds (Figures 2 and 3).
Figure 1. Slip map of the Taron Earthquake. Source: USGS
Figure 2. Detailed slip map of the Taron earthquake. Source: USGS
Figure 3. Source time function, describing the rate of moment release with time after the Taron earthquake origin. Source: USGS.
Because of its occurrence at a depth of about 100 km, this earthquake did not trigger a significant tsunami. A tsunami measuring less than 1 metre struck the coast of New Ireland shortly after the earthquake. Many residents in the northern parts of the autonomous region of Bougainville sought higher ground amid warnings that tsunami waves were possible. A nurse at Buka General Hospital in Bougainville said the quake was so strong it felt like the building she was sleeping in would topple. She said patients were being moved a few kilometres to higher ground. Due its remoteness from land, there were no immediate reports of damage, although it caused a blackout in the town of Kokopo at the northeastern tip of New Britain. Nevertheless, despite their considerable depth, earthquakes of this kind occurring within subducted slabs can generate damaging ground motion levels, as occurred during the 1993 Mw 7.9 Kushiro earthquake beneath southeastern Hokkaido, Japan, which generated peak ground accelerations of about 0.35g in Kushiro. The large spatial extent of the earthquake is indicated in the shakemap shown in Figure 4, with MMI intensity VIII (PGA of 22%g) extending from Rabaul, New Britain across southern New Ireland to Sahano, Bougainville.
Figure 4. Shakemap of the Taron earthquake. Source: USGS.