Performance of slopes in past New Zealand earthquakes : literature review and lessons learned from historical earthquakes

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Hancox, G.T. 2015 Performance of slopes in past New Zealand earthquakes : literature review and lessons learned from historical earthquakes. Lower Hutt, N.Z.: GNS Science. GNS Science report 2015/16 62 p.

Abstract: This report provides a detailed literature review of coseismic landsliding and performance of slopes and during historical earthquakes in New Zealand. Earthquakes considered in the review comprise twenty two events between 1848 and 1995 which caused significant earthquake-induced landsliding, including: Wairarapa 1855, Arthurs Pass and Murchison (Buller) in 1929, Napier (Hawkes Bay) 1931, Wairarapa in June and August 1942, Inangahua 1968, Edgecumbe 1987, and Arthurs’s Pass 1994 and 1995. Nine other important coseismic landslide events that occurred between 2003 and 2015 were also reviewed. These comprise earthquakes in Fiordland in 2003 and 2009, Rotoehu 2004, Christchurch in 2010 and 2011, Cook Strait and Lake Grassmere 2013, Eketahuna 2014, and the Wilberforce Valley in 2015. The first part of the report defines the locations and parameters of these earthquakes, describes the extent and main effects of the landsliding for each event, lists the main references and sources of information relating to the landsliding that occurred, and provides a summary of the results and relationships determined in previous studies of historical earthquake-induced landsliding in New Zealand. These relationships include associations with factors such as earthquake magnitude, Modified Mercalli (MM) shaking intensity, slope angle, rock and soil types, and the area (km2) over which landsliding occurred. More recent studies have shown, however, that the number, size, and density of landslides appears to provide a better measure of the severity and significance of landsliding during earthquakes. The second part of the report describes and discusses the main findings and lessons learned from studies of landslides and slope failures that have occurred during historical earthquakes in New Zealand, and the implications for cut slope design, and performance of cut slopes during strong earthquake shaking in the future. The main issues that are discussed and illustrated include: the occurrence of slope failures; landslide types and mechanisms; the size of landslides and consequences to infrastructure, buildings (including loss of life); and the influence of ground conditions (soil and rock types), topography, and seismogenic factors on the areas over which landslides occur and their resulting effects and damage. (auth)