Seismic History of the Luganville Region, Vanuatu

Vanuatu lies along the Pacific Ring of Fire at the convergent boundary between the Pacific and Australian plates. The region experiences frequent large earthquakes due to active subduction along the New Hebrides trench, where the Australian plate descends beneath the Pacific plate at rates exceeding 10 cm per year. This tectonic setting produces both shallow crustal events and deeper intraslab seismicity, with the island of Espiritu Santo, home to Luganville, situated directly above the subduction interface.

On 4 October 2000 at 16:58 UTC, a magnitude 7.0 earthquake struck 29 km west-northwest of Luganville at a depth of 23 km. The event caused strong shaking across Espiritu Santo and prompted local evacuations, though major structural damage remained limited. Since the start of 2000, the area within roughly 85 km of this epicenter has hosted multiple additional magnitude 7 or greater earthquakes, underscoring the persistent seismic hazard.

Notable events include a magnitude 7.1 quake on 9 January 2001 located 16 km northeast of Port-Olry, a magnitude 7.2 event on 1 August 2007 situated 56 km east of Luganville, and a magnitude 7.1 shock on 20 October 2015 positioned 31 km northeast of Port-Olry. Further activity occurred on 28 April 2016 with a magnitude 7.0 earthquake 3 km northwest of Norsup, followed by a magnitude 7.0 event on 8 January 2023 located 23 km west-northwest of Port-Olry. An additional magnitude 7.3 earthquake took place 48 km east-northeast of Luganville on 30 March 2006.

These earthquakes share similar source characteristics, with depths typically between 10 and 70 km and focal mechanisms consistent with thrust faulting on the plate interface. The close spacing of epicenters reflects segmentation of the subduction zone and episodic release of strain accumulated through plate convergence. Historical records and paleoseismic studies indicate that comparable sequences have recurred over centuries, highlighting the long-term potential for strong ground motion in northern Vanuatu.

Ongoing monitoring by regional seismic networks continues to track aftershock sequences and background seismicity, supporting improved hazard assessment for communities around Luganville and Port-Olry.