The Andaman Sea was formed by the movement of tectonic plates, creating structures like an accretionary prism and outerarc ridge. The accretionary prism is made up of fault slices and folds from materials scraped off the subducting Indian Plate. The western slope is steep, while the eastern side has faulted anticlines and synclines. The width of the deforming portion of the accretionary prism narrows towards the north. The West Andaman Fault divides the sea into a shallow forearc and a deeper backarc region. The Diligent Fault in the forearc basin is actually a compressional feature.