This article explores social media use during Japan's 2011 earthquake. In the era of social media, this earthquake provides an opportunity for analysing the role of communication during a crisis. To explain how social media use transforms the locus of crisis communication, we collected sufficient data on tweets in Japan from the Twitter public timeline during the earthquake and examined the Japanese government's Twitter account and its URLs. The results indicate that crisis communication on Twitter was led by peer-to-peer communication and relied on peer-generated information. In addition, the government's traditional leadership role in exercising tight control over crises and facilitating disaster communication was not clearly apparent on Twitter. By examining the shift in the locus of crisis communication through social media, this study provides new insights into the current use of social media.