1. A method, comprising: receiving a search request for an online post; determining, from the search request, a target place and a target range of distance from the target place; retrieving one or more online posts that were posted from a posting location within the target range and that include in their content a word associated with the target place; identifying respective posting locations from which the one or more retrieved online posts were posted, based at least in part on location information of a device via which each of the one or more retrieved online posts were respectively posted; determining respective reliabilities of the one or more retrieved online posts based at least in part on the word associated with the target place and the posting location from which the corresponding retrieved online post was posted, respectively, wherein the respective determined reliabilities decrease as a distance between the target place and the posting location increases; presenting, as a response to the search request, the one or more retrieved online posts, excluding retrieved online posts whose respective determined reliabilities are lower than a predetermined value; monitoring a variation in an amount of online posts from within the target range of distance from the target place; and estimating an incident time and an incident place of an incident occurrence when the amount of online posts posted from within the target range increases suddenly.