The 1999 Ambrym earthquake occurred on November 26 at 00:21:17 local time with a moment magnitude of 7.4 and a maximum Mercalli intensity of VII (Very strong). The back arc thrust event occurred within the Vanuatu archipelago, just to the south of the volcanic island of Ambrym. Vanuatu, which was previously known as New Hebrides, is subject to volcanic and earthquake activity because it lies on an active and destructive plate boundary called the New Hebrides Subduction Zone. While the National Geophysical Data Center classified the total damage as moderate, a destructive local tsunami did result in some deaths, with at least five killed and up to 100 injured.

This was one of very few events along the New Hebrides Subduction Zone that has been studied. Scientists from technical institutes in the region submitted papers to the scientific journals about the event, and while not all data on each of the aspects of the event are in agreement, what is certain is that the d'Entrecasteaux Ridge is producing unusual effects where it infringes into the subduction zone via the Indo-Australian Plate.