On 29 September 2009, a tsunami devastated the Samoan and northern Tongan islands. Here, an unusual earthquake sequence that preceded this tsunami is analysed. A magnitude-8.1 intraplate faulting event in the outer trench-slope at the northern end of the Tongan subduction zone was followed by extensive interplate faulting, with total moment equivalent to that of a magnitude-8.0 earthquake. Overlap of the seismic signals had obscured the fact that distinct faults had ruptured with different geometries.
- Thorne Lay
- Charles J. Ammon
- Alexander R. Hutko
