Seismic Activity in Northern Vanuatu: The 2009–2010 Earthquake Sequence

Vanuatu lies along the tectonically active New Hebrides subduction zone, where the Australian Plate converges with the Pacific Plate at rates exceeding 10 cm per year. This setting produces frequent large earthquakes and has shaped the islands’ volcanic arc geology over millions of years. The northernmost islands, including the Torres group near Sola, sit directly above the subducting slab and experience both interplate thrust events and intraslab normal-faulting earthquakes.

Between 7 October 2009 and 27 May 2010, five earthquakes of magnitude 7.2 or greater struck within 200 km of Sola. On 7 October 2009 at 23:13 UTC, a magnitude 7.4 event occurred 143 km northwest of Sola at a depth of 31 km. Within hours, three additional magnitude 7+ events were recorded in the same region: a magnitude 7.8 event 196 km northwest of Sola, another magnitude 7.8 event near the Santa Cruz Islands approximately 60 km from the main shock, and a magnitude 7.7 event 148 km northwest of Sola. A magnitude 7.2 earthquake followed on 27 May 2010, located 100 km west-northwest of Sola. These closely spaced events illustrate the capacity of the subduction interface and adjacent slab to rupture in rapid succession.

The 31 km focal depth of the 7 October 2009 magnitude 7.4 main shock placed it within the seismogenic portion of the plate interface, consistent with typical thrust mechanisms observed throughout the New Hebrides arc. The cluster of large aftershocks within tens of kilometres of one another reflects stress transfer along both the megathrust and steeply dipping normal faults within the downgoing slab. Historical records show that similar sequences have occurred in northern Vanuatu, underscoring the region’s persistently high seismic hazard.

No fatalities were reported from the 2009–2010 sequence, largely because the epicentral areas lie offshore and population density on the Torres Islands remains low. Nevertheless, strong ground shaking was felt across northern Vanuatu, and minor structural damage occurred on nearby islands. The events also generated small tsunamis that were recorded at regional tide gauges but caused no significant coastal inundation.

Ongoing GPS measurements confirm continued convergence across the subduction zone, indicating that elastic strain continues to accumulate. Seismic monitoring by regional networks remains essential for rapid characterisation of future events and timely tsunami warnings for Vanuatu’s northern provinces.

References

USGS Earthquake Catalog (events 2009–2010)
Global CMT Catalog
Pacific Tsunami Warning Center archives