Kaikōura Earthquake Short-Term Project : landslide inventory and landslide dam assessments

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Massey, C.I.; Townsend, D.B.; Dellow, G.D.; Lukovic, B.; Rosser, B.J.; Archibald, G.C.; Villeneuve, M.; Davidson, J.; Jones, K.E.; Morgenstern, R.; Strong, D.T.; Lyndsell, B.M.; Tunnicliffe, J.; Carey, J.M.; McColl, S. 2019 Kaikōura Earthquake Short-Term Project: landslide inventory and landslide dam assessments. Lower Hutt, N.Z.: GNS Science. GNS Science report 2018/19. 43 p.; doi: 10.21420/G2FP82

Abstract:

The MW 7.8 14 November 2016 Kaikōura Earthquake generated more than 20,000 mapped landslides and about 200 significant landslide dams. Besides the immediate hazard from the landslides, cracked ground, landslide debris and landslide dams also pose longer-term risk to infrastructure, because if the landslides and debris remobilise and the dams breach, they could generate future debris flows and floods. These in turn, could sever transport routes and further damage infrastructure, adversely impacting the post-earthquake economic recovery of the region. The goal of this short-term project was to collect perishable (ephemeral) data on landslides and landslide dams generated by the earthquake. Currently there are more than 20,000 landslide source areas in the landslide inventory. Key findings from the landslide inventory are: 1) the number of large landslides (with source areas ≥10,000 m2) triggered by the Kaikōura Earthquake is fewer than the number of similar sized landslides triggered by other similar magnitude earthquakes in New Zealand; 2) the largest landslides (with volumes from 5 to 20 M m3) occurred either on or within 2,500 m of the 24 mapped faults that ruptured to the surface; and 3) the landslide density within 2,500 m of a mapped surface fault rupture is as much as three times higher than those densities farther than 2,500 m from a ruptured fault. Around 200 significant landslide dams generated by the earthquake have now been mapped and combined with data from past New Zealand and overseas landslide dams. These data have been used to develop a regional-scale, empirically-based tool to assess the post-formation likelihood of dam failure (breaching), which can be used for future landslide dam generating events. Many of the larger dams have also been investigated in detail and dam-breach models have been calibrated from back-analysing their failure. (auth)