A model for fracturation in the Loyalty Islands

Abstract

The Loyalty Islands are a series of limestone karstified islands that are currently uplifted and deformed on the elastic bulge of the Australian plate before its subduction at the Vanuatu trench (SW Pacific). These islands have been extensively surveyed for geology and hydrogeology, and fracturation maps have been produced which indicate a major direction N 110 ± 35 ° . This fracture orientation is analytically modeled as resulting from the elastic deformation of the Australian lithosphere before its subduction. First, the vertical deflection around a circular subduction zone is determined. Second, a point force is introduced which accounts for the first stages of a collision between the Loyalty ridge and this circular subduction zone. This model yields principal stress orientations and elevations of the islands in fair agreement with real data.