A FEW times a year, Mexico City is rocked by tremors strong enough to cause tall buildings to sway and lights to flicker on and off. Most of the time they cause little damage fake oakleys ebay, but sometimes they are devastating: in 1985, nearly 20,000 people were killed after a magnitude 8.0 earthquake struck the city.

On April 3rd the city’s government launched a mobile-phone application that will give citizens about a minute’s notice of impending quakes. So far available only for BlackBerry, the free app will emit a “Seismic Alert” in the form of a sound when an earthquake is on its way. Your correspondent is already considering trading in his iPhone.

Mexico City has quite a good early-warning system for earthquakes, because the tremors that strike the capital tend to originate near the coast, a couple of hundred miles south. The quakes travel at about 7,000 miles (11,250 km) per hour, which means it takes more than a minute and a half for a rumble in Acapulco to work its way up to Mexico City (where it tends to cause more damage, owing to the soggy former lake-bed on which the capital is built).

This blog has footage of a session in Congress on March 20th, when the city was hit by one of the most violent earthquakes since 1985. (Fortunately, no deaths were reported.) You can see that after the alarm goes off, the politicians have nearly a minute to get out before the lights start swaying and flickering.

The problem is that most people are not within range of one of the early-warning loudspeakers, meaning they are denied this head start. Of course fake oakleys, by no means everyone has a BlackBerry either. But if this technology can be extended to other types of mobile phone, Mexico City will be much better prepared for the next big earthquake—and there is no doubt that one day it will come.