M 7.0 earthquake beneath the island of Melampa in the Vanuatu island chain of the southwest Pacific Ocean occurred as a result of thrust faulting on or near the boundary between the Australia and Pacific plates. The preliminary location, depth and focal mechanism of the event indicate rupture occurred on an east-dipping thrust fault consistent with the location and orientation of the subduction zone interface at depth in this region. The earthquake is located nearly 100 km to the east of the New Hebrides Trench, the bathymetric expression of the plate boundary between the Australia and Pacific plates, where lithosphere of the Australia plate subducts into the mantle beneath the North Fiji Basin. At the location of this earthquake, the Australia plate moves east-northeast with respect to the Pacific plate at a velocity of approximately 84 mm/yr.

The Vanuatu region frequently experiences large earthquakes; 23 events of M 7 or larger have occurred within 250 km of the April 28, 2016 event over the preceding century. The largest was a M 7.7 earthquake in May 1965, 130 km to the north of the April 28 event. The April 28 event also follows a sequence of moderate-sized earthquakes roughly 200 km to the northwest, the largest of which was a M 6.9 earthquake on April 3rd. To date, that sequence involved 48 events of M 4.5 or greater, including the April 3 M 6.9 event, two M 6.7 earthquakes and one M 6.4 shock. Because of the remote location of these earthquakes, few have caused any significant damage or fatalities