Spectra and peak ground accelerations for the assessment and rebuilding of structures in Christchurch were revised rapidly following the magnitude 6.2 earthquake on 22 February 2011. The NZS1170.5:2004 hazard factor Z for Christchurch was quickly raised from 0.22 to 0.3. There have been different requirements for different purposes: spectra for the design of new structures and the assessment of existing ones, and peak ground accelerations for liquefaction assessments and for evaluating the probabilities of rock falls in the Port Hills. Particularly challenging has been the need to take into account the time-varying nature of a productive 

on-going earthquake sequence. The increased design levels recognise that the motions in Christchurch were abnormally strong, the strongest that have been recorded in any New Zealand earthquake. Ground motions around the CBD were enhanced by factors of about 2 or more from median values given by local and US groundmotion prediction equations for the magnitude and distance of the earthquake. The recorded CBD  motions were generally about double the 500-year design motions for Christchurch. Systematic effects such as enhanced stress-drop, rupture-directivity, site effects and basin effects are being modelled.