Just before 5.20 am on Sunday 21 August 2011 (6.20 pm on Saturday 20 August, GMT) a large earthquake occurred roughly 40 km south-southwest of the Island of Efate, Vanuatu. This was recorded as a magnitude 7.0 quake at a depth of 28.5 km by the United States Geological Survey and a magnitude 7.4 magnitude quake at a depth of 36 km by the Vanuatu Meteorological Services. This was followed by a magnitude 5.0 quake an hour later. The Pacific Tsunami Warning Centre did not issue an ocean-wide tsunami alert, but did warn of the possibility of a local tsunami; the Vanuatu Meteorological Services also issued a tsunami waring. A small tsunami wave, just over 1 m high was observed on Efate about an hour after the initial quake. The tsunami warning has now been lifted; there are no reports of any damage or casualties on Efate.
The location of the quake.
Vanuatu is a chain of 80 volcanic islands on the boundary between the Pacific and Australian plates. The Australian plate is being subducted beneath the Pacific at a rate of 9 mm a year, making the area highly prone to earthquakes. There are 13 active volcanoes in the islands, although there is none on Efate, despite it being thought to be less than 3 million years old. The nearest is North Vate on Nguna Island, 6 km to the north.