This paper presents a novel method to estimate characteristics of information sources about a topic by analyzing their information diffusion subnetworks in blogspace. In an information diffusion network, each influential information source has an affected subnetwork whose nodes are reachable from it. We define three information diffusion properties of the subnetwork using the numbers of three types of directed 2-edge connected subgraphs, which are basic structures in a directed acyclic graph such as an information diffusion network. Each type of basic structure is related to information scattering, information gathering, or information transmission. We visualized and analyzed the structure of information diffusion networks extracted for other topics. Furthermore, we characterize the information diffusion properties by using the rank correlation coefficient, precision, and mean reciprocal rank (MRR) and mean average precision (MAP) of three types of information sources: official sites, news sites, and CGMs. We found that the three information diffusion properties have different characteristics and give priority to different types of information sources.