Co-seismic and ongoing land deformation at Mt Lyford Village, North Canterbury

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Langridge, R.M.; Townsend, D.B. 2018 Co-seismic and ongoing land deformation at Mt Lyford Village, North Canterbury. Lower Hutt, N.Z.: GNS Science. GNS Science miscellaneous series 120. 17 p.; doi: 10.21420/G21M10

Abstract: The Mw 7.8 2016 Kaikōura earthquake caused considerable damage to land and buildings at Mt Lyford Village, north Canterbury. In light of this event, the Natural Hazards Research Platform (NHRP) along with the Hurunui District Council (HDC) and Environment Canterbury (ECan) have jointly funded a study of the earthquake damage caused to Mt Lyford Village. This project was designed by these stakeholders and the Department of the Prime Minister and Cabinet (DPMC) and led by GNS Science (GNS). GNS built a team that included expertise in engineering geology, structural engineering and log cabin engineering with members from Golder Associates Ltd. and PTL (NZ) Ltd. The results of the project have been presented as a GNS Science Consulting Report (Langridge et al., 2018; GNS CR 2017/227) along with GIS map layers to HDC. That report has been followed up by a GNS Science Letter Report (Langridge & Townsend, 2018; GNS CR 2018/104 LR) that details how the application of Land Classes could assist future planning decisions. The key findings of these two reports are: Post-earthquake field reconnaissance and follow-on science using post-earthquake airborne LiDAR led to the evaluation of new locally-relevant land classes based on slope and erosion criteria, and to active fault avoidance zones. The Land Classes are: Mt Lyford Land Class 1 (i.e. ML LC 1): slopes of <25°, and outside of any other land class definition, including active fault avoidance zones; ML LC 2: a mixed slope class, having a combination of very steep (≥25° slope), and less steep slopes (<25°); ML LC 3: comprising land with slopes of >25° (very steep slopes); ML LC 3a: comprising a ±20 m wide setback zone around the upper edge of ML LC 3 areas; and ML LC 4: comprising areas related to pre-existing landslide deposits Land Class ML LC 4 was established because mapping in the Langridge et al. (2018) report highlighted that large landslide deposits may be susceptible to future movement or re-mobilisation and may be susceptible to material falling onto them from their own headscarp area. Active faults have been mapped and buffered for fault avoidance according to the MfE guidelines relating to building on or adjacent to active faults (Kerr et al., 2003). The recommended treatment of areas within each of these land classes and their associated risk profiles are discussed in the GNS Letter Report (Langridge & Townsend, 2018). Engagement with the community of Mt Lyford has occurred frequently before, during and after the response investigations, and has been one of the most important and successful components of this project. The project team, encompassing GNS, HDC, ECan and Golder Associates have been involved in engagement in a united way, providing certainty for the villagers of Mt Lyford. (auth)