"There was a seven or eight-fold increase in tweets overnight after the earthquake," said Twitter spokeswoman Kaori Saito in Tokyo. "Some people had trouble finding reliable information, so we've tried to make it easier to search for accounts run by local governments."
Last year Twitter created "lifeline" accounts operated by local Japanese towns and cities, which users can search for using their postal codes. The company has held "disaster drills" to help users tweet useful information during emergencies, and Japan's Fire and Disaster Management Agency is mulling allowing "911" calls to be placed through Twitter when phones go down.
The sheer number of Twitter messages sent out during and after a disaster can also serve as a source of data. Researchers at the University of Tokyo have said they can detect when earthquakes are occurring with 96 percent accuracy by filtering Twitter messages for certain keywords and frequency.
Google also became a trusted online source in the months after the quake. Its "Person Finder" site became the national database for information on those caught in the disaster and eventually swelled to over 600,000 entries. The site was repeatedly featured by national broadcaster NHK as a public resource and received data from the National Police Agency, local governments and newspapers. Google has since launched services such as "public alerts" that allow users to quickly find local info on earthquakes and other disasters.
The search giant, Twitter and other online companies have pledged to work more closely in future disasters. In September of last year Google helped organize a "big data workshop" to analyze information from the 2011 earthquake. Google provided data on search trends and Twitter supplied a week of Twitter messages from after the disaster. Honda supplied data such as car location information from its online navigation system.
Facebook is still not as popular in Japan as in other countries and has faded in recent months. But the number of accounts increased about six times since before the earthquake and is currently between 13 million and 14 million, according to an analysis published by Japan's Ceraja Technology and Socialbakers in the U.S.
Many of the government support agencies and nonprofit agencies that sprung up in the aftermath of the disaster say they use Facebook as their main portal to reach users.
"At the time [after the earthquake] Facebook was the way we kept in touch privately. People couldn't use their phones, and it was the easiest," said Takahiro Chiba, an official who organizes volunteers in the eastern seaside town of Kessenuma, where tsunamis washed huge ships ashore and caused massive oil fires.
"Now it's more for public groups, for posting notices and information about our activities. Volunteers are still coming, and this is how we reach them."
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