Agricultural land rehabilitation following 2010 Darfield (Canterbury) earthquake

Abstract

This paper describes the nature of earthquake damage and rehabilitation of rural land affected by fault rupture and liquefaction following the 4 September 2010 Darfield (Canterbury) Earthquake. Remediation of land damaged by fault rupture and liquefaction was a significant concern for affected farmers and land-owners. A multidisciplinary team of researchers linked to the Rural Recovery Group (responsible for recovery of rural areas following the Canterbury earthquake) used a variety of techniques to assess land damage and evaluate the effectiveness of various rehabilitation techniques. It was found that land damage caused by strike slip fault rupture could generally be repaired by heavy roller. In areas of severe surface deformation and fracturing, deep cultivation followed by rolling was necessary to close surface fractures and flatten fault micro-topography to restore the land to a useable condition for agricultural use. Liquefaction damage to land consisted of blistered topography (by liquefied sediment injecting between topsoil and sub-soil) and liquefied sediment ejection at the surface. Both surfaces were often unsuitable for continuing agricultural operations. Several passes by a rotary-hoe and power-harrow effectively smoothed blisters and returned paddocks to a suitable state. Land severely affected by sediment ejection required scraping or grading of the sediment to < 50 mm and cultivation of the material into the topsoil. Both treatments resulted in destruction of current pasture or crop. Land less severely affected could be treated by spreading only, which conserved the existing pasture. Future work will track the on-going recovery of remediated and un-remediated land.