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The Tonga-Kermadec trench, which separates the subducting Pacific plate from the overthrusting Indo-Australian plate, is intersected at~ 26 S by the Louisville Ridge seamount chain. The collision zone is characterized by a 3000 m reduction in trench depth, a 15 anticlockwise rotation of the trench axis, a 20% reduction in the width of extensional bend faulting on the Pacific plate and a rough, hummocky, forearc on the Indo-Australian plate. These morphological characteristics are accompanied by a 40% reduction in seismicity compared to regions immediately to the north and south. The influence of subducting seamounts on megathrust processes is not limited to their immediate vicinity and there is evidence of morphological and seismological manifestations in the forearc with wavelengths similar to the wavelengths of the flexural moats and bulges that flank these features. The Louisville Ridge collision zone has …