Earthquakes in Vanuatu are frequent and are sometimes accompanied by tsunami, though these events are not often destructive. The archipelago, which was formerly known as New Hebrides, lies atop a complex and active plate boundary in the southwestern Pacific Ocean.
Overall, the population in this region resides in structures that are highly vulnerable to earthquake shaking, though some resistant structures exist. Most buildings in Vanuatu are constructed with lumber.
The primary tectonic feature of the island chain is the New Hebrides Trench, the convergent boundary between the Australian and Pacific plates. Along the WadatiâÂÂBenioff zone, earthquake activity has been observed as shallow, intermediate, and deep-focus events at depths of up to . Volcanic activity is also present along this north-northwest trending and northeast-dipping subduction zone.
While much of the island arc experiences intermediate-depth earthquakes along a WadatiâÂÂBenioff zone that dips steeply at 70ð, the area adjacent to the d'Entrecasteaux Ridge does not. There is a corresponding gap in seismicity that occurs below where it enters the subduction zone from the west. According to the NUVEL-1 global relative plate motion model, convergence is occurring at roughly per year. The uncertainty, which also affects the Tonga arc, is due to the influence of spreading at the North Fiji Basin. Of the 58 M7 or greater events that occurred between 1909 and 2001, few were studied.
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