2002 Sandaun earthquake
On 9 September 2002, at 04:44:23 PGT, a 7.6 earthquake struck off the coast of Sandaun Province in Papua New Guinea. The largest earthquake to hit mainland Papua New Guinea since 1938, this shallow reverse earthquake damaged or destroyed hundreds of homes and buildings in Sandaun and East Sepik Provinces, mainly in the town of Wewak, killing six people and injuring 70 others. A local tsunami measuring high also caused damage to homes in the region.
Tectonic setting
The island of New Guinea lies within the complex zone of collision between the Australian plate and the Pacific plate. Within this overall setting, the active tectonics of northern Papua New Guinea is dominate by the effects of continuing collision between the Huon–Finisterre island arc terrane with the edge of the Australian continental margin. The overall shortening is concentrated into two zones of thrust faulting, the Ramu–Markham fault zone, which forms the southwestern boundary of the Huon–Finisterre terrane, and the Highlands Thrust Belt, which lies further southwest and deforms the Australian margin. The hanging wall of the Ramu–Markham thrust system is broken up by a series of strike-slip faults. The orientation of these faults, parallel to the direction of thrusting, suggests that they accommodate distortion of the Huon–Finisterre block. Most of the seismicity in northern Papua New Guinea is associated with the Ramu–Markham fault system, with a smaller number of earthquakes occurring on the strike-slip faults and on the Highlands Thrust Belt.Earthquake
The earthquake was the largest in mainland Papua New Guinea since 1938. The United States Geological Survey reported a magnitude of 7.4, 7.6 or 7.7. It was caused by a rupture on a low-angle thrust fault in the New Guinea Trench, with the rupture occurring on a steep, northwest-striking reverse fault or on a moderately dipping, southeast-striking reverse fault. A fault measuring in length, and wide ruptured with a maximum slip of. A Modified Mercalli intensity of X was estimated, with MMI VI shaking recorded in Wewak, Kairiru, Ambunti and Angoram in East Sepik, and Aitape in Sandaun; MMI IV-V was estimated to have been felt in Keerom and Jayapura in eastern Indonesia. ShakeMap perimeters estimate that shaking may have been felt as far away as the towns of Lae and Kerema.By the end of 2003, 109 aftershocks measuring 4.0 or higher were recorded, including three above 6.0, with most of them occurring east-southeast of the mainshock along the estimated rupture zone. The strongest aftershock measured 6.3 and struck southwest of the mainshock on 16 September. A 6.2 event also struck Marienberg Rural LLG in February 2003. Additionally, there were 36 foreshocks preceding the mainshock, including a 6.2 event in October 2001, and a 6.7 event near Aitape in January 2002 that killed one person and destroyed 450 structures.