Establishing a disaster mitigation planning is an urgent issue in Japan where people are facing the high risk of a devastating earthquake. We need to utilize various information for supporting quick and safe wide-area evacuation. This is especially important for densely built-up wooden residential areas where many building collapse and big fires are presumed. For instance, the locational information and the route information of evacuation areas will contribute for quick and safe evacuation. Also, the information of the fire-spreading and street-blockages is expected to reduce the risk of fire-exposure. As the means to obtain the information such as fire-spreading or street-blockages, Social Network Services (SNS) by portable terminals will have the great potential. They might enable us to acquire various and real-time information efficiently and effectively. However, there are many issues to be discussed for acturalizing the evacuation surpport system by SNS. These include the quality and accuracy of information and robustness of the information network. Under the situation with difficulty in using SNS and in getting the information through portable terminals, not only bulletin boards but also the information-hearsay among evacuees are expected to play an important role. Even if the information is scattered by the information-hearsay between evacuees, however, incorrect information may be generated and adversely affect on evacuation. We need to investigate the influence of information-hearsay on wide-area evacuation in a situation of the incorrect information outbreak, for realizing quick and safe evacuation.
In this paper, we construct a model that describes the information-hearsay and the wide-area evacuation behavior of evacuees immediately after a large earthquake occurs. Using the model, we evaluate quantitatively the effects of the information-hearsay on evacuation time and safety of evacuation routes. The principal novel findings about the influence of information-hearsay on wide-area evacuation are as follows;
(1) In areas where most people are unfamiliar with geographical information, the unuseful information is repeatly exchanged through the information-hearsay of evacuees. This is because that the limited number of people have correct information about the locational information of evacuation areas. As a result, the evacuation time and the risk of evacuation may increase.
(2) If a few guides who are familiar with areas start guidance immediately after a large earthquake occurs, the correct information spreads through the information-hearsay between evacuees and may greatly reduce the evacuation time and the risk of evacuation.
(3) If the guides share the information each other, they can instruct and support evacuees using the latest and wide-area information, and not only the risk of evacuees but also the risk of themselves can be reduced.
Next, we construct a model that describes the process of the generation of incorrect information by the misrecognition in order to inspect how the incorrect information affects on the wide-area evacuation, and obtain some new findings as follows;
(1) In case of high probability of misrecognition, the incorrect information around the evacuation areas spreads out and may affect on the wide-area evacuation, since many evacuees need the information around the evacuation areas.
(2) In areas where population density is high, the correct information is scattered and evacuation becomes effective. However, under the condition in which much incorrect information is generated, it is scattered rapidly and immediately after a large earthquake occurs, and this results in affecting on the evacuation time and the risks of evacuation.
