This study examines Twitter users' behavioral response to the Fukushima nuclear power plant disaster, namely with regards to the credibility of third-party information shared during the disaster. In the study, 4,950 individual tweets from 2,156 users were categorized, and it was found that generally, changes in proximity to the disaster correlate with a change in the degree to which low-credibility sources are cited. Specifically, users from within Japan were less likely to share information from low-credibility sources, implying a higher sense of social responsibility by those close to the disaster. It was also found that, despite non-disclosure of location correlating with an increase in sharing of information from low-credibility sources, Japanese tweeters, who were typified by location non-disclosure, did not share this sharing tendency. Implications from an online behavior perspective are discussed.