Woodlark plates

The Solomon Islands subduction zone

There are three plates being subducted along the Solomon Islands subduction zone: the Solomon Sea plate, the Woodlark plate, and the Australian plate. The Solomon Islands subduction zone is noted for producing an unusual pattern of earthquakes called "doublets". These are two earthquakes of similar magnitude that occur close to each other in space and time. Most of the historic doublets in the Solomon Islands have occurred north of the 2007 earthquake in the vicinity of Bougainville Island and along the New Britain subduction zone. The largest of these doublets are a pair of M=8.0 and 8.1 earthquakes that occurred 12 days apart in 1971. The portion of the fault that ruptured in the first earthquake of the 1971 doublet reruptured in a different manner during a M=7.7 earthquake in 1995. Other doublets have occurred in 1919 and 1920, 1945 and 1946, and 1975 (both occurred in the same year), all in the M=7-8 range. In the southeastern part of the Solomon Islands subduction zone, there were doublets in 1931, 1939, and a triplet in 1977 (Lay and Kanamori, 1980). It is unclear what mechanism causes earthquake doublets to occur, although stress triggering from the first earthquake of the doublet is likely a significant a factor.

Over geologic time, ridge subduction contributes to the uplift of the overriding plate and the creation of islands such as Simbo, Gizo, and Ranunga very near the Solomon trench. As ridges are subducted, scars in the overriding plate called "re-entrants" are left that can often be identified in the bathymetry and seismic reflection profiles. Many of these processes can affect tsunami generation.

See: http://walrus.wr.usgs.gov/tsunami/solomon07/index.html