M 7.1 - 16 km NE of Port-Olry, Vanuatu

  • 2001-01-09 16:49:28 (UTC)
  • 14.928°S 167.170°E
  • 103.0 km depth

Tectonic Summary

The January 9, 2001, M 7.1 Vanuatu earthquake occurred as the result of oblique reverse faulting at intermediate depth within the subducting Australia plate, approximately 100 km beneath the island of Vanuatu in the Pacific Ocean. The focal mechanism solutions for the earthquake indicate that oblique rupture occurred on either a steep north-south reverse fault or a near-vertical east-west reverse fault. Slip on a fault of either orientation is consistent with the intraplate compressional tectonics implied by the faulting mechanism and earthquake depth. At the location of the earthquake, the Australia plate moves to the east-northeast with respect to the Pacific plate at a velocity of about 117 mm/yr, subducting at the New Hebrides Trench west of the January 9th earthquake. The western edge of the Pacific plate can be subdivided into smaller microplates, such as the New Hebrides microplate in the region of this event.

Earthquakes with focal depths between 70 and 300 km are commonly termed “intermediate-depth” events. Intermediate-depth earthquakes represent deformation within subducted slabs rather than at the shallow plate interface between subducting and overriding tectonic plates. They typically cause less damage on the ground surface above their foci than is the case with similar-magnitude shallow-focus earthquakes, but large intermediate-depth earthquakes may be felt at great distance from their epicenters. “Deep-focus” earthquakes, those with focal depths greater than 300 km, also occur beneath the North Fiji Basin, but are thought to be associated with a detached fragment of subducted Australia plate, rather than with active subduction from the New Hebrides Trench, which reaches depths of close to 300 km. Earthquakes have been reliably located to depths of about 650 km in this region. The Vanuatu region experiences a very high level of earthquake activity, with more than a dozen events of M 7 or larger recorded since the early decades of the 20th century within 400 km of the January 9th event. Recent large earthquakes include a M 7.5 earthquake in November 1999 that occurred approximately 200 km to the southeast of the January 9th event.

Hayes et al. (2016) Tectonic summaries of magnitude 7 and greater earthquakes from 2000 to 2015, USGS Open-File Report 2016-1192. (5.2 MB PDF)

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