Detailed pattern analysis of liquefaction surface ejection in an alluvial setting: Lessons from the Canterbury earthquake sequence

Abstract

The 2010 -2011 Canterbury earthquake sequence has provided an opportunity to study how liquefaction correlates with different sedimentary environments. Our results demonstrate that liquefaction surface manifestation at two sites in a floodplain setting was mainly located on highertopographic areas such as crevasse splays or scroll bars ridges. However, in the crevasse splay the potential liquefiable layer we identified was part of a channel fill sequence within an abandoned meander partially buried by the crevasse splay. In an inner meander setting, the source layers of the liquefied sands is associated with sediments that form the scroll bar itself. Our study focuses on liquefaction in the alluvial environment along the Halswell River (Greenpark, 5 km South-West from Lincoln). We aim to establish a correlation between landforms affected from liquefaction and their sediment architecture. The first site (Hardwick) is an old river channel overlaid by a crevasse splay deposit, and the second site (Marchand) is an inner meander belt; both were severely affected by liquefaction during the Darfield and Christchurch earthquakes. At each site we: (1) mapped the distribution of liquefaction and alluvial geomorphic features with DEMs derived from LIDAR; (2) undertook Ground Penetrating Radar surveys; (3) dug several trenches to expose the surficial stratigraphy and liquefaction features; and (4) retrieved 18 m of core sediments to look for the liquefiable layers. We also collected samples for radiocarbon, microscopic sediment fabric and grain size analysis. Nine seismic cone penetration tests were also carried out to at least 12 m to reveal the geotechnical properties and explore the sediment architecture of the deeper sediments. The lessons learned about the influence sediment architecture on the patterns of liquefaction during the Canterbury sequence will be applied in future paleoliquefaction studies , helping to improve assessments of liquefaction potential and seismic hazard across the country.