Ground motions and damage observations in the Marlborough region from the 2013 Lake Grassmere earthquake

Abstract

This paper presents various aspects of the preliminary damage observations caused by ground motions in the Marlborough region following the Mw6.6 Lake Grassmere earthquake on 16 August 2013. To emphasize the severity of the ground shaking, the observed pseudo-acceleration response spectra are compared to those from the 21 July 2013 Mw6.5 Cook Strait earthquake and the NZS1170.5:2004 design spectrum. The near-source damage to State Highway 1 roads, bridges and buildings is presented within. Stainless steel wine storage tanks showed various damage states that were consistent with observations from previous earthquake events. The performance of wine tanks and other winemaking infrastructure are discussed with future design considerations. Eleven water storage dams within 12 kilometres of the earthquake source were inspected and preliminary observations are discussed. A 250,000 cubic metre dam located 10 kilometres southwest of Seddon suffered moderate damage following the 21 July event while significant further damage was sustained following the 16 August event and emergency earthworks were undertaken to reduce the risk of dam failure (to those living downstream). The performance of residential housing in rural townships of Seddon and Ward was satisfactory with respect to preserving life safety however there was moderate levels of damage which are presented within. Post-earthquake business disruption was minimal as commercial buildings in the Blenheim central business district sustained either minor or no damage.