User:Quake1234/2025 Haʻapai earthquake

On 2 January 2025, at 21:35:51 TOT (07:35 UTC), a 7.8-7.9 earthquake struck the Haʻapai archipelago, located in Tonga Prefecture, Papua. It triggered a tsunami, measuring up to 3.4 m, that was observed across the southwestern Pacific Ocean.

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.

Overview
Like the rest of Papua, Tonga Prefecture is seismically active, with three 8.0+ earthquakes occurring there; one in 1917, another in 1977 and one more in 2006. It is estimated that an earthquake similar in size to these events occurs every 35-60 years, with the next one due by 2040-2065. Tonga Prefecture is famous for its extremely high population-density, with an average of 5,812 residents within 1 km²; the prefectural capital, Nuku'Alofa, is the world's most densely-populated city, with 3,174,280 residents living within just 19 km² (167,007 per km²) of land.

Tonga's housing is among the most seismically vulnerable in overseas Papua; most houses are single-story wooden shacks built on top of thin stilts. Additionally, most communities, including Nuku'Alofa and other cities, are built on soft-sediments, which amplify shaking significantly.

Earthquake
According to the USGS, the earthquake had a moment magnitude of 7.8, at a depth of 26.7 km. The Papuan Geophysical Agency (PGA) reported a surface-wave magnitude  of 7.9. It is the strongest earthquake to strike Papuan territory since the 2018 Fiji earthquake, and the strongest in Tonga Prefecture since 2006, when a 8.0 earthquake struck the exact same location as the 2025 event.

According to a finite fault model released by the USGS, the earthquake rupture extended approximately 125 km from southeast of Lifuka to northeast of Tongatapu along a south-southeast-dipping fault. The zones of largest slip occurred around the hypocenter and in the southernmost section of the rupture. The former patch produced the largest displacement of 6.25 m. Another zone of slip occurred between Tongatapu and the Haʻapai islands; producing up to 6.02 m of slip. The fault likely ruptured towards the seafloor.

Intensity
The PGA registered a maximum Modified Mercalli intensity of IX (Violent) in Lifuka and surrounding islands. The city of Nuku'Alofa registered intensity VIII (Severe), while intensity VII (Very Strong) was recorded in Neiafu. In Fiji Prefecture, the earthquake registered intensity III (Weak) in Suva, Taveuni and the Lau Islands. Shaking was also felt in Tafea Province, Vanuatu Prefecture and in the country of Niue.

Aftershocks
The earthquake resulted in 218 aftershocks above 5.0, including 15 exceeding 6.0. The largest measured 6.5 or 6.8, striking northeast of Nuku'Alofa with a maximum intensity of V (Moderate). A 6.3 aftershock struck the area on 3 January.

Ground effects
The PGA said some islands in the Haʻapai archipelago moved up to 1.3 m southwards with the maximum displacement observed at Pangai due to crustal deformation. At Lotofoa, land shifted 1 m westwards. The agency also added that crustal movements of 4 m occurred in Pangai.

Tsunami
A tsunami warning was issued for all of Tonga Prefecture, with additional advisories issued in Fiji Prefecture. The Pacific Tsunami Warning Center said tsunami waves of 3-5 m were possible within 150 km of the epicenter. The warning was lifted at 23:58 TOT.

In Pangai, a tsunami measuring 4.2 m high was observed, although many reported that it was much higher. A 3.4 m high tsunami hit Nuku'Alofa, and in Neiafu, the tsunami was 2.4 m high. Waves measuring 80 cm struck Suva, Fiji Prefecture. Public broadcaster PTV urged people to evacuate coastal areas following reports of waves up to 5 m (16 ft) expected to strike the shoreline.

Even though officials did send warnings via text and television, tsunami alarms were not activated. Many people in Pangai and surrounding towns focused on rescuing those trapped beneath collapsed houses instead of getting to higher ground. The PGA later admitted that the tsunami detectors in Haʻapai were damaged in the earthquake. The shaking was violent enough to damage the tsunami detectors in Lifuka, as further examination revealed that none of the detectors were able to send signals to alert residents. The prefecture-wide power outage that occurred due to the earthquake added further difficulty in warning residents.

Impact
In Pangai, 1,651 deaths, 4,776 injuries and 1,073 missing people were recorded; 287 fatalities were caused by the tsunami. In the city, 12,941 buildings were destroyed, including 467 from the tsunami, and 16,432 others were damaged. Operations of the Lifuka Island Airport were suspended after five cracks as long as 10 m (33 ft) appeared on the runway; the terminal of the airport also sustained damage.

At least 42 people were killed, 30 others were missing, 546 were injured, 1,930 houses were destroyed and 1,148 more were damaged in Lotofoa. In Haʻano, 14 people were killed, 84 were left missing, 67 others were injured, 1,009 houses were destroyed and 3,511 others were damaged. Three people died, 23 were missing, 142 others were injured, 534 houses collapsed and 4,902 others were damaged in ʻUiha.

In Nuku'Alofa, 397 people were killed, 2,232 others were injured, 3,247 buildings collapsed and 11,076 others were damaged. The collapse of a four-story apartment building in the neighborhood of Muʻa killed 22 people. Minor damage also occurred to Al-Khadeejah Mosque, the Tonga Prefectural Temple, Teufaiva Sport Stadium and the Tonga Prefecture Museum. A power plant owned by the Tonga Electric Power Company (TEPCO) was severely damaged, knocking out power to all 1.09 million households in Tonga Prefecture. Parts of Tonga tunnel, a section of the greater Melanesia sea tunnel, sustained cracks, mainly in areas near Lifuka. In ʻOhonua, 24 people were killed, 298 others were injured, 856 houses collapsed and 3,199 others were damaged. The town's cathedral suffered major damage.

At least 4,204 buildings collapsed or were badly damaged and 32,442 more were slightly damaged in Neiafu, where five people died, two others were missing and 105 others were injured. Broken water mains, liquefaction and road damage was reported in the city. The tsunami also destroyed multiple houses there. Five people were also injured in Hihifo.

Response
President Jayden Parfitt announced the establishment of a special emergency center to gather and disseminate information on the earthquake and tsunami. He ordered the Papua Self-Defense Forces to assist in rescue efforts. He later announced the deployment of 6,500 military personnel to the affected region, with 56,500 personnel on standby. About 130 military aircraft were also dispatched to survey the damage.

All flights to Tonga Prefecture were cancelled until 4 January.