This paper aims to show empirical evidence of how media and ICT (Information and Communication Technology) motivate people to take after-quake initiatives such as collecting information, preparing for another disaster and participating in volunteer activities and making donations. Assuming that information provided by media and ICT is purely rational and influential because irrelevant information is discarded, the impact of the media information is to be analysed in conjunction with direct and indirect influences of the disaster and the existence of communities. The Great East Japan Earthquake hit the northern part of Japan on March 11, 2011. Some sixteen thousand lives were lost and three thousand people are still missing as of May 23, 2012. One of the distinct features of the earthquake with respect to the role of ICT and media is that television and other image media provided plentiful high-resolution visual images of the earthquake and the subsequent tsunami to other people. In addition, social networking services performed important role providing and exchanging information among people by complementing the role of mass media. In contrast, voice calls on mobile phones, the most popular communication means, were pretty much useless in terms of establishing communication due to heavy traffic on telephone lines. In the paper, the rationality of media information is defined as the “Pythagorean Effect” as it can be compared to his addiction to “rational numbers”. People faced with such information are assumed to be more motivated to take immediate action after the disaster. Structural equation modelling was applied to construct a model to examine the impact of media information. An online questionnaire survey was carried out over sample panels pre-registered in a survey research company. The result implies that media information has a different contribution to post-quake behaviour as compared to real experience in that it triggers information gathering while damages from the earthquake provoke countermeasures against possible aftermath. They both have the same influence on altruism. In addition, real communities motivate people to collect information. In contrast, virtual communities induce altruistic behaviour.