1996 Biak earthquake
The 1996 Biak earthquake, or the Irian Jaya earthquake, occurred on 17 February at near Biak Island, Indonesia. The earthquake, which occurred on the New Guinea Trench, had a moment magnitude of 8.2 and a maximum Mercalli intensity of IX. The run-up height of the generated tsunami reached. The disaster left at least 108 people dead, 423 injured, and 58 missing. It damaged or destroyed 5,043 houses which subsequently made another 10,000 homeless. At Korim, 187 houses were destroyed. Various countries and organizations provided aid and relief in the aftermath of the earthquake.
Tectonic setting
New Guinea lies within a very complex tectonic regime surrounded by microplates which accommodate the collision and oblique convergence between the Australian plate and the Pacific plate. In the north, the Caroline plate and North Bismarck plate subduct underneath the Bird's Head plate and the Woodlark plate along the New Guinea Trench. The earthquake occurred at the central portion of the trench. The western portion of New Guinea has parallel subduction zones to the north and south of it along a continuation of the Philippine Trench and a convergent boundary between the Bird's Head plate and the Banda Sea plate. In western central New Guinea, the Maoke plate has multiple boundaries with various plates. At the far eastern portion of the island, the South Bismarck plate interacts with the Woodlark plate, as well as the Solomon Sea plate subducting underneath the Woodlark plate. The largest on-land plate boundary in the region, however, is between the Woodlark plate and the Australian plate. Though generally considered largely aseismic before this earthquake, this region of the New Guinea Trench may have experienced a similar large earthquake in 1914.Earthquake
Focal mechanisms indicate shallow-angle reverse faulting which is consistent with a subduction zone rupture. It ruptured an area long and wide along the New Guinea oceanic trench with an average slip of. From the hypocenter, the rupture propagated to the west before propagating another east, ~15 seconds later. The largest slip was ~ near the hypocenter. Large aftershocks struck the area, with various focal mechanisms. The mainshock may have triggered nearby seismic structures to activate. Aftershocks were most common in the areas with the highest slip from the mainshock.Tsunami
At Madori, on the west coast of Biak, a run-up of was measured, while at Korem in northern Biak, waves were up to. The tsunami also affected parts of nearby islands, including Yapen, Owi, and Pai, where waves of were measured. Roughly five minutes after the shaking, nearby residents heard an extraordinarily loud sound, such as one from an airplane, which they understood as a signal that a large wave was approaching. The local coastal population fled for higher ground as result. This action is credited with saving many lives from the tsunami.The tsunami produced was larger than expected for the size and location of the earthquake. A localized submarine landslide was a plausible explanation for the strong waves in western Biak. This is further supported by the west coast of Biak being struck by the tsunami first, despite facing away from the main tsunami source. This does not align with a traditional shallow earthquake rupture tsunami, which further lends credence to the theory of a submarine landslide in the area near Madori. Multiple landslides were reported in the area near the maximum run-up height.