1 Introduction Online social media (OSM) are Internet sites where people can interact freely, share their thoughts and engage in conversation, using words, audio, images and video . These services allow individuals, organizations and governments to create, exchange content and disseminate information with large numbers of people without geographic constraints. It appears in many forms including blogs and microblogs, wikis, social networks, virtual words, forums and message boards, media sharing sites, and social bookmarking. There are numerous famous sites such as Facebook, Twitter, YouTube, Wikipedia, Reddit, Flickr, Instagram and many more. On March 11, 2011, the most powerful earthquake hit the Tohoku region with a magnitude of 9.0, triggering a catastrophic situation in Japan, which killed more than 18,000 people [1]. Immediately after the earthquake there were interruptions in electricity, water supply and computer networks [2]. The use of email and mobile phone calls are not permitted due to the breakdown of telecommunications links and access control. However, OSM services using 3G mobile Internet data were accessible. In disaster situations, OSMs are useful and are becoming increasingly popular as sources of information and communication channels with family and friends to exchange information on each other's safety conditions [3]. Twitter, Facebook and Mixi are the three main forms of social media used during and after the 2011 Great East Japan Earthquake [3] [4]. A survey of social media used after the earthquake indicates that most users are more interested in using Twitter than Mixi and Facebook, with 63.9% of them believing that Twitter helps them gather information about the disaster [4] . The purpose of this paper is ...... half of the paper ...... Special Workshop on the Internet and Disasters (SWID '11), ACM, New York, Article 3, (2011).[16] Tanaka, Y. and Sakamoto, Y., Matsuka, T., “Transmission of Rumor and Criticism on Twitter After the Great Japan Earthquake,” Annual Meeting of the Cognitive Science Society, p. 2387 (2012).[17] Mukai, M., “Research on a Model for Decision Making in Retweets That Caused the Spread of False Rumors in Emergencies,” Master's Thesis, Graduate School of Software and Information Science, Iwate Prefectural University (2012 ). [In Japanese] [18] Mukai, M., Nishioka, D., Saito, Y., Murayama, Y., “A study on a retweet model for a guideline for Twitter use in emergencies,” The 30th Symposium on Cryptography and Information Security (SCIS 2013), (2013). [In Japanese] [19] “English Definition of Action.” Retrieved from: http://www.oxforddictionaries.com/ [Date accessed: 2013/12/15]