Seismic performance of two water-storage dams during the Mw 6.6 Lake Grassmere Earthquake in August 2013

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On 16 August 2013, a magnitude Mw 6.6 earthquake occurred 35 km south-east of Blenheim in the South Island, New Zealand. It was a shallow earthquake which had a hypocentre at a depth of 8 km below ground. The epicentre of the earthquake is at about 9 km southeastern of the Seddon. This paper discusses the seismic performance of two water storage dams used to store water for irrigation purposes. The dams are located within 10 km of the earthquake epicentre. They are earth-fill embankments, each about 12 m high. The dams were designed and constructed within the last nine years. Relatively large deformation, cracking and slumping occurred as a result of the earthquake. Post-earthquake studies comprising surveys of the embankments and geotechnical investigations were undertaken to evaluate the possible cause of damage and to provide remediation plan. The results indicate poor construction with some design deficiencies contributed to the damage.