Building on innovative frameworks for analysing and visualising the tweet data available from Twitter, developed by the authors, this paper examines the patterns of tweeting activity which can be observed in the aftermath of the Feb. 2011 Christchurch earthquake. Local and global responses to the disaster were organised around the hashtag #eqnz, which averaged some 100 tweets per minute in the hours following the earthquake. The paper identifies the key contributors to the #eqnz network and shows the key themes of their messages. Emerging from this analysis is a more detailed understanding of Twitter and other social media as key elements in the overall ecology of the media forms used for crisis communication. Such uses point both to the importance of social media as a tool for affected communities to self-organise their disaster response and recovery activities, and as a tool for emergency management services to disseminate key information and receive updates from local communities.