Tectonic Summary

The January 13, 2011, M 7.0 Loyalty Islands earthquake occurred as the result of shallow normal faulting within the Australia plate, in the region of the boundary between the Australia plate and the Pacific plate. Focal mechanism solutions indicate that rupture occurred on either a steeply dipping, southeast-striking normal fault or on a more shallowly dipping, northwest-striking fault. At the location of the earthquake, the Australia plate moves east-northeast relative to the Pacific plate at a velocity of about 80 mm/yr The Australia plate subducts beneath the Pacific plate at the New Hebrides Trench immediately east of the January 13th earthquake and is seismically active to a depth of 300 km. The stresses that generated the earthquake result from the bending of the Australia plate during this subduction beneath the Pacific plate. Slip on a fault aligned with either nodal plane of the focal mechanism solution is consistent with this intraplate setting.

The western margin of the Pacific plate that lies to the east of the New Hebrides Trench is commonly viewed as being subdivided into several microplates that move relative to each other at rates of a few centimeters per year, whose differential motions help to accommodate the overall convergence between the Australia and Pacific plates. These include the New Hebrides microplate local to this earthquake.

The New Hebrides Arc region of the Australia/New Hebrides plate boundary experiences numerous strong earthquakes. In the past quarter century, the 1,000-kilometer section of the arc centered near the epicenter of the January 13th earthquake has produced 19 earthquakes of M 7+. The largest was a M 7.7 earthquake near the southern end of this section in May 1995, which caused no recorded damage or casualties.

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)

Event Details

Event Map

Tectonic Summary

Historical Magnitude 4.5+ (100km)

Tectonic Summary

Historical Magnitude 4.5+ (100km)