Collection of disaster-related information by focusing on Twitter posts immediately after retweeting announcement posts

Utilizing Twitter posts during and after a disaster situation has been gaining attention since the Great East Japan Earthquake of 2011. There have been numerous studies pertaining to the collection of disaster-related information from Twitter posts using keywords or hashtags. To obtain disaster-related information, we focus on tweets posted immediately after retweets of a disaster-related announcement post. In this study, we analyze “sample posts” that were tweeted as a result of the Ogasawara Islands off the West Coast Earthquake of 2015.