The M 7.3 July 7 2013 earthquake northeast of Papua New Guinea occurred as the result of normal faulting approximately 380 km deep within the subducted Australia Plate. 200km to the south of this event, the Australia Plate subducts beneath the Pacific plate at the New Britain Trench, moving towards the north-northeast at the rate of 103 mm/yr. The depth and faulting mechanism of the July 7 earthquake are consistent with the event resulting from internal (intraplate) deformation of the subducted slab, rather than as an interplate event on the shallow plate boundary interface.
Crustal tectonics of the New Britain region are commonly described in terms of relative-motions of microplates that are situated at the boundary of the Australia and Pacific plates. The New Britain Trench region is familiar with large earthquakes; this subduction zone is one of the most seismically active regions of the world. Deep earthquakes (>300km) are reasonably common as well; several M > 6.5 earthquakes have occurred within 250km of the July 7 event over the past 40 years, including a M 6.8 event in an almost identical location in June 1995.
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