The 2009 Mw 7.8 earthquake on the Puysegur subduction zone produced minimal geological effects around Dusky Sound, New Zealand

Abstract Post-earthquake field surveys in Dusky Sound, the region overlying the downdip end of the rupture patch of a MW 7.8 Puysegur subduction zone earthquake, have shown only localised physical evidence of a tsunami and minimal coastal deformation. Following the 15 July 2009 earthquake, eye-witnesses and tide gauges recorded a near-field tsunami and GPS stations showed evidence of land subsidence of up to 220 mm. We investigated these effects over a series of three field visits. One month after the event a tsunami deposit consisting of gravel, sand and shell was identified at only one site, despite searching at various coastal environments around Dusky Sound. We attribute this localisation of tsunami effects to site features that amplified the tsunami waves and the unusual (for this rocky coastline) availability of unconsolidated shoreface sediment at that site. Repeated visits to the Dusky Sound area at one, five and eight months after the earthquake have found no evidence of a landward shift in the i...