Agence France Presse (AFP)
By Sylvain Estibal
Sirens wailed across Mexico City late Thursday warning its estimated 20 million population of a rapidly approaching quake from the Pacific, the latest use of its effective early warning system.
By the time alarmed residents felt the first shockwaves from the 8.2 magnitude quake, many had already made it onto the streets or into parks, well away from trembling and swaying buildings.
For the past two decades, Mexico's seismic alert system, known by the initials CIRES, has provided the city with an early warning of disaster, using a hundred sensors placed along its Pacific coast, where the risk of an earthquake is greatest.
It can take a minute for seismic waves from a quake's epicenter to reach the capital, several hundred kilometers away. Even at that distance, Mexico City is vulnerable because it sits on an ancient lakebed and the relatively loose soil makes it prone to severe shaking.