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On 21 July 2024, at 18:05:22 PGT (08:05 UTC), an earthquake of 8.9 struck 74 km north-northwest of Wewak, the capital and largest city of East Sepik Province, Papua. The megathrust-faulting earthquake occurred with a hypocenter depth of 14.2 km, rupturing the Sepik Megathrust.

The earthquake was the sixth-largest ever recorded since 1900, the strongest in Papuan history, and globally the largest earthquake since the 2011 Tōhoku earthquake. It was also the largest earthquake recorded during 2024.

Tectonic setting
The primary tectonic feature of the 1200 km island chain is the New Hebrides Subduction Zone, the convergent boundary of the Indo-Australian and Pacific Plates. Along the Wadati–Benioff zone, earthquake activity has been observed as shallow, intermediate, and deep-focus events at depths of up to 700 km. Volcanic activity is also present along this north-northwest trending and northeast-dipping oceanic trench.

While much of the island arc experiences intermediate-depth earthquakes along a Wadati–Benioff zone that dips steeply at 70°, the area adjacent to the d'Entrecasteaux Ridge does not. There is a corresponding gap in seismicity that occurs below 50 km where it intrudes into the subduction zone from the west. According to the NUVEL-1 global relative plate motion model, convergence is occurring at roughly 8 cm per year. The uncertainty, which also affects the Tonga arc, is due to the influence of spreading at the North Fiji Basin.

Earthquake
The USGS reported a magnitude of 7.9, which was later revised to 8.8. It occurred at a depth of 32.5 km. The PGA put the earthquake's magnitude at 7.9, before being revised to 8.4 and later 8.9.

Tsunami
A tsunami warning was issued by the PGA at 18:11 PGT for East Sepik, Madang and Sandaun Provinces, with the PGA saying that waves up to 6 m could hit the coast. Advisories were also issued for Morobe and Manus Provinces. At 18:56, after the PGA revised the earthquake's magnitude to 8.9, the warning expanded to Morobe, New Britain and Manus Provinces.

The Pacific Tsunami Warning Center issued a local tsunami watch for the Alaskan and Hawaiian coasts, but said a large wave was unlikely.

East Sepik
At least 42 people were injured, 21 houses collapsed, 3,000 others, 16 health centers, six schools, and two bridges were damaged and power outages occurred in Karawari.

Highlands
A section of the Porgera Gold Mine collapsed, killing two miners and injuring 19 others. In Ialibu, four people killed, 120 others were injured, 300 houses were destroyed, 600 others and several historical buildings were damaged.

Morobe
In Menyamya District, one person was killed, 28 houses were destroyed and 60 more were damaged. A landslide in Kariba Municipality buried part of a farm, killing over 40 livestock.

Moresby
In Port Moresby, 68 people were hospitalized and over 2,000 buildings were damaged. Power outages left about 40% of the city, including the city center, without electricity for up to an hour. Some power lines also reportedly fell in rural areas.

In Kairiku, 17 people were injured, 14 houses collapsed and 272 others, 22 public buildings, five temples and a bridge were damaged. Seventeen people were also injured in Rigo. Four people were injured, a temple collapsed and 285 structures were damaged in Hiri.

Oro
Two people were injured in Kira.

Milne Bay
Over 500 houses were damaged or destroyed in Alotau.