Papua New Guinea

Papua New Guinea is one of the most seismically active countries on Earth, experiencing more large earthquakes per unit area than almost anywhere else, owing to its position at the intersection of the Indo-Australian, Pacific, and several microplates in one of the world's most complex tectonic configurations. The New Britain [[subduction-zone]] carries the Solomon Sea Plate beneath the South Bismarck microplate; the Trobriand Trough and the Woodlark Basin record active seafloor spreading; the New Guinea Highlands represent an ongoing continental collision between the Australian craton moving northward and the accreted oceanic terranes of the island's north coast. Active subduction occurs on all sides of the main island: the Manus subduction zone to the north, the New Britain arc to the east, and the western tip of the island approaches the Halmahera and Sorong fault systems. The result is that virtually every region of Papua New Guinea experiences significant seismicity, and multiple magnitude 7 and 8 earthquakes have struck in the modern era. The Highlands, home to over two million people in valleys at elevations of 1,500 to 2,500 metres, are crossed by multiple active faults and experience some of the country's most damaging onshore earthquakes.

The historical record of large earthquakes in Papua New Guinea extends back well into the twentieth century and reveals an almost relentless succession of major events. The 1935 Rabaul earthquake sequence (magnitude 7.0) preceded volcanic activity. The 1951 Manus Island earthquake (magnitude 7.9) was one of the largest ever recorded in the country. The 1975 Morobe earthquake (magnitude 7.0) caused damage in the Markham Valley. A magnitude 8.0 earthquake struck the New Ireland region in 1995. The 2 March 1987 Madang earthquake (magnitude 7.1) killed 10 people and triggered major landslides. The 17 July 1998 Sissano [[tsunami]] disaster resulted from a magnitude 7.0 submarine landslide-triggered tsunami that struck the Aitape coast without warning, killing approximately 2,200 people and destroying three coastal villages — one of the deadliest [[tsunami]]s in the twentieth century. The 26 February 2018 Highlands earthquake (magnitude 7.5) struck the Southern Highlands and Hela provinces, killing at least 125 people, destroying thousands of homes, and triggering massive landslides that buried communities and cut roads across a mountainous region with very limited infrastructure.

The tectonic setting of Papua New Guinea is among the most complex in the world. The island of New Guinea sits on the advancing northern edge of the Indo-Australian Plate, which is converging northward toward the Pacific Plate at rates of 100 to 110 millimetres per year — the highest convergence rate of any continental-scale boundary. This collision has thickened the crust beneath the Central Range to create the Owen Stanley and Star Mountain ranges. To the north, a series of oceanic arcs, plateaus, and basins have been accreted to the Australian margin over the past 50 million years, building outward from the continent. Active back-arc spreading in the Woodlark Basin and Manus Basin means new ocean floor is being created even as old ocean floor is being consumed on the opposite side. The New Britain [[subduction-zone]] is one of the world's fastest subduction systems, consuming the Solomon Sea Plate at up to 150 millimetres per year. [[aftershock]] sequences after major PNG earthquakes are typically extensive and energetic; the 2018 Highlands sequence produced hundreds of felt events over several months. The country lacks a dense national seismological network, and many earthquakes in remote Highlands areas go unrecorded at the local level.