May 20, 2023 Earthquake: Loyalty Islands, New Caledonia

A tsunami was generated with the following recorded wave heights in centimeters: 14 at Ouinne, 12 on Mare, 11 on Lifou and 3 at Thio, New Caledonia.

The May 20, 2023, M 7.1 earthquake southeast of the Loyalty Islands occurred as a result of normal faulting near the plate boundary interface between the Australia and Pacific plates. Focal mechanism solutions indicate the earthquake occurred on either a moderately-dipping normal fault striking to the east or on a moderately-dipping normal fault striking to the west. At the location of this earthquake, the Australia plate converges with the Pacific at a rate of approximately 75 mm/yr. At the South New Hebrides Trench, Australia lithosphere sinks beneath the Pacific plate, descending into the mantle and forming the New Hebrides/Vanuatu subduction zone, stretching from New Caledonia in the south to the Santa Cruz Islands in the north.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Normal faulting events of the size of the May 20, 2023, earthquake are typically about 45x20 km (length x width).

The May 20, 2023, M7.1 earthquake occurred 23 hours following a M7.7 earthquake located approximately 33 km to the east. The Loyalty Islands region is very active seismically, and the region within 250 km of the May 20, 2023, earthquake has hosted 13 other M 7+ earthquakes over the preceding 50 years. The largest events prior to this sequence were an M7.7 on February 10, 2021, and an M 7.7 earthquake on May 16, 1995. Because of their remote locations, earthquakes in this region as less likely to create strong shaking in populated areas.

More information about the tectonics of the Tonga-Kermadec subduction zone is available on this story map.

Reference #13456:

Tectonic Summary

The May 20, 2023, M 7.1 earthquake southeast of the Loyalty Islands occurred as a result of normal faulting near the plate boundary interface between the Australia and Pacific plates. Focal mechanism solutions indicate the earthquake occurred on either a moderately-dipping normal fault striking to the east or on a moderately-dipping normal fault striking to the west. At the location of this earthquake, the Australia plate converges with the Pacific at a rate of approximately 75 mm/yr. At the South New Hebrides Trench, Australia lithosphere sinks beneath the Pacific plate, descending into the mantle and forming the New Hebrides/Vanuatu subduction zone, stretching from New Caledonia in the south to the Santa Cruz Islands in the north.

While commonly plotted as points on maps, earthquakes of this size are more appropriately described as slip over a larger fault area. Normal faulting events of the size of the May 20, 2023, earthquake are typically about 45x20 km (length x width).

The May 20, 2023, M7.1 earthquake occurred 23 hours following a M7.7 earthquake located approximately 33 km to the east. The Loyalty Islands region is very active seismically, and the region within 250 km of the May 20, 2023, earthquake has hosted 13 other M 7+ earthquakes over the preceding 50 years. The largest events prior to this sequence were an M7.7 on February 10, 2021, and an M 7.7 earthquake on May 16, 1995. Because of their remote locations, earthquakes in this region as less likely to create strong shaking in populated areas.