‘Seismic alert!’: Apps warn Mexicans of quakes

Mexico City: A powerful earthquake strikes off the Pacific coast of Mexico. Within seconds, radio transmissions, megaphones and smartphone apps blare warnings to the capital's 20 million people before the ground shakes.
After the loud "seismic alert!" alarm, Mexico City residents have as much as a minute to flee their homes, offices and schools before buildings start to sway.
But such technology was not available on September 19, 1985, when a massive 8.1-magnitude coastal quake rocked the metropolis, crushing buildings and killing thousands.
It can take more than a minute for the seismic waves to reach the capital hundreds of kilometers away. But once they arrive, buildings start moving back and forth because the soil below -- a former lake bed -- is soft.
When the country marks the 30th anniversary of the tragedy on Saturday, the early-warning systems will be switched on during a national drill.
For two decades, a civil association known by its initials CIRES has provided the city with a system that automatically interrupts radio broadcasts and triggers alarms inside buildings thanks to some 100 sensors placed along the western coast.
For the first time this year, the alarm will sound on 8,200 street megaphones.
The surge of smartphone technology now gives Chilangos, as the capital's residents are known, the ability to receive warnings in the palm of their hands with apps such as SkyAlert and Alerta Sismica DF. Within two seconds that a quake hits, SkyAlert's sensors send a broadband signal to phones, triggering a loud sound with a voice that repeats "seismic alert" and a message indicating the temblor's intensity.