The city of Mercer Island has joined Twitter, an online social messaging utility. According to city Communications Coordinator Joy Johnston, the new media will allow residents — once registered on Twitter — to follow and contribute to city news, announcements and emergency information. The latter purpose, Johnston emphasized, is especially important.

“Twitter takes only a few seconds for an update — it’s really instant. So it’s a good way to reach people, particularly when dealing with an emergency,” Johnston said.

The city’s first Twitter messages were posted during last week’s “Island Quake 2009” emergency drill.

On April 30, the city reenacted what would occur if a 6.7 magnitude earthquake hit Mercer Island in order to practice its new City Emergency Management Plan. The two-hour long drill, which included all city emergency response personnel, as well as the school district, community center and civic volunteers, was documented on the city’s Web site in event-by-event Twitter updates. The sequence of “Tweets,” as the 140-character messages are called, from “Mercer Island cut off from region” at 10:22 a.m. to “Emergency water well activated” at 11:45 a.m., can still be viewed on the city Web site’s emergency preparedness page.

As communication coordinator, Johnston will be responsible for posting Twitter messages on behalf of the city. So far, the city has two Twitter followers. Johnston hopes more will join.

“We hope that citizens can follow the city. [Posts] won’t be minute to minute, but I’ll use it for critical things that are happening, such as updates on the I-90 closures,” the city employee said, adding that anyone can “Tweet” updates from their cell phones, laptops and computers.

The city Twitter project is currently in an experimental phase. Members of the Mercer Island School District, local businesses, organizations and hundreds of Island residents already have Twitter accounts. Registration and usage are free.