Figure 2.

(a) An illustration of the focused themes of activity foci in the OSN of day 6. (b) Densities of daily networks (black dots) and activity foci (boxes and colourful dots). (c) The proportion of existing social ties in OSNs during the disasters (see Material and methods). (d) The distribution and mean of weights of social ties in each OSN. There are two types of social ties with regard to the neighbourhoods of the connected users: the social ties connect the users from the same neighbourhood (orange), and the social ties connect the users from different neighbourhoods (blue). The weights of social ties were obtained by the frequency of communications between two users.