Social media such as Twitter is playing a more and more important role in sharing information and coordinating disaster responses. However, after the 2011 Tohoku earthquake in Japan, Twitter users transmitted rumors about radiation and supplies, which Social media such as Twitter can play an important role in sharing information and coordinating disaster response. However, after the 2011 Tohoku earthquake in Japan, Twitter users transmitted rumors about radiation and supplies, which caused unnecessary panic. In the current work, we examined the thinking behind the decision to spread disaster-related tweets in Twitter. We showed subjects tweets related to the 2011 Tohoku earthquake. For each tweet, we asked them whether or not they would retweet it and the reason for their retweeting decision. Whereas thought of others (e.g., informative to others) played a major role when they decided to retweet, consideration of self (e.g., not interesting to me) dominated when they decided not to retweet. We further examined how factors such as source, familiarity, and importance of disaster-related tweets affect the retweeting decisions. Our results suggest techniques for minimizing the spread of false information during responses to disasters.