Insights from Liquefaction Ejecta Case Histories from Christchurch, New Zealand

Liquefaction ejecta were a primary contributor to the damage of land and light-weight structures in Christchurch from the 2010–2011 Canterbury earthquakes. It occurred predominantly in east Christchurch, which is typically characterized by thick, clean sand deposits. By contrast, ejecta tended to be absent in the stratified silty soil swamp deposits of west Christchurch. To advance understanding of ejecta production, 235 well-documented case histories of ejecta occurrence, its quantity, and its effects on infrastructure were developed. The ejecta database includes 61 sites that underwent four major earthquakes that produced no-to-extreme ejecta. The case histories take advantage of numerous CPTs, boreholes, pre-and post-earthquake airborne LiDAR surveys, aerial photographs, liquefaction land damage documentation from insurance claims, and earthquake-specific PGAs and groundwater estimates. Ejecta coverage and amounts for each of the four main Canterbury earthquakes were extracted using photographic-and LiDAR-based approaches because direct measurements of ejecta quantities were not made. The database provides the basis for the development of procedures to evaluate the occurrence and quantity of ejecta.