How Social Media Construct "Truth" Around Crisis Events: Weibo's Rumor Management Strategies After the 2015 Tianjin Blasts

China's control of information online is often imposed by social media platforms in the name of rumor management. This article examines the content moderation strategies of Sina Weibo, China's largest microblogging platform, in regulating discussion of rumors following the 2015 Tianjin blasts. More than 100,000 Weibo posts were collected and categorized into three data sets: rumor discussion posts from the public, rumor-debunking posts from Weibo's official rumor rebuttal accounts, and posts removed from the system. Two content-moderation rumor strategies, namely rumor rebuttal and content removal, were identified. Clustering analysis and time series analysis was applied to test how these two strategies were used to filter posts of different topics and how they were associated with public discussion of rumor-related topics. Our findings suggest that the platform's response to rumor varied depending on the political sensitivity of the topic. Time-series analysis indicated that the implementation of both strategies was usually associated with a subsequent increase in general discussion about the rumor, suggesting that these strategies do not create a consistent chilling effect on public speech.