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Very strong and shallow M7.7 earthquake hits southeast of Loyalty Islands, small tsunami produced

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A very strong earthquake registered by the USGS as M7.7 hit southeast of Loyalty Islands, New Caledonia at 02:57 UTC on May 19, 2023. The agency is reporting a depth of 37.7 km (23.4 miles). EMSC is reporting M7.7 at a depth of 30 km (18.6 miles).

The epicenter was located 333.5 km (207.2 miles) E of Vao, South Province, New Caledonia, and 435.5 km (270.6 miles) SSE of Isangel, Tafea, Vanuatu.

16 000 people are estimated to have felt light shaking and 4 000 weak.

Based on preliminary earthquake parameters, hazardous tsunami waves are possible within 1 000 km (620 miles) of the epicenter along the coasts of Vanuatu, New Caledonia and Fiji, PTWC said at 03:02 UTC.

Tsunami waves reaching 0.3 to 1 m (1 – 3.3 feet) above the tide level are possible for some coasts of Vanuatu, the agency said at 04:29 UTC.

Tsunami waves are forecast to be less than 0.3 m (1 foot) above the tide level for the coasts of American Samoa, Australia, Chuuk, Cook Islands, Fiji, French Polynesia, Howland and Baker, Jarvis Island, Kermadec Islands, Kiribati, Kosrae, Marshall Islands, Nauru, New Zealand, Niue, Palmyra Island, Papua New Guinea, Pohnpei, Samoa, Solomon Islands, Tokelau, Tonga, Tuvalu, Wallis and Futuna, and New Caledonia.

Actual amplitudes at the coast may vary from forecast amplitudes due to uncertainties in the forecast and local features, PTWC said. In particular, maximum tsunami amplitudes on atolls and at locations with fringing or barrier reefs will likely be much smaller than the forecast indicates.

The following are tsunami wave observations from coastal and/or deep-ocean sea level gauges at the indicated locations. The maximum tsunami height is measured with respect to the normal tide level:

Thio, New Caledonia recorded a height of 0.07 m (0.2 feet) at 04:09 UTC with a wave period of 20 minutes; Lenakel, VU measured a height of 0.45 m (1.5 feet) at 04:02 UTC with a wave period of 4 minutes; Mare, New Caledonia observed a height of 0.19 m (0.6 feet) at 04:13 UTC with a wave period of 6 minutes; Ouinne, New Caledonia registered a height of 0.20 m (0.7 feet) at 04:06 UTC with a wave period of 8 minutes; and Lifou, New Caledonia documented a height of 0.12 m (0.4 feet) at 04:00 UTC with a wave period of 6 minutes.


The USGS issued a Green alert for shaking-related fatalities and economic losses. There is a low likelihood of casualties and damage.

Overall, the population in this region resides in structures that are highly vulnerable to earthquake shaking, though some resistant structures exist. The predominant vulnerable building types are unknown/miscellaneous types and wood construction.

Recent earthquakes in this area have caused secondary hazards such as tsunamis that might have contributed to losses.

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Estimated population exposure to earthquake shaking

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Selected cities exposed

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Regional seismicity

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May 20, 08:49 UTC

The mainshock was followed by at least 56 moderate to strong aftershocks over the next 30 hours, including M7.1 at 01:51 UTC and M6.5 at 02:09 UTC on May 20.

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Featured image credit: TW/SAM, Google


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