By Diarmuid O'Dea
Mexico has one of the only three earthquake early warning systems on the globe. It was needed after its calamitous 1985 Mexico City earthquake killed approximately 10,000 persons and injured over 30,000.
Like the Pacific Northwest of North America there is a significant subduction zone on the west coast of Mexico. Small earthquakes in the the three states that border the coast are common. Most alarming is the possibility of a significant earthquake and its impact on Mexico City 350 kilometres to the east. The following video by Al-Jazeera explains how the system works.
Mexico City, a city of nearly 10 million persons, is built on the silt left behind from an ancient lake. Simply put, while the distance from the coast should decrease the impact but the silt beneath the city actually amplifies S-Waves such that the they rebound off the bedrock beneath the silt and regain velocity and destructiveness. This geological aspect to Mexico City makes it very susceptible to disastrous consequences from an otherwise moderate earthquake that originates from a great distance. This phenomenon should concern other inland cities and towns on the west coast of North America.
The Mexican system is founded on 100 plus seismic sensors strategically placed on the coast and communicated through TV, radio, sirens and cell phones. The system was tested in 2014 by a moderate earthquake in Mexico City and delivered an early warning that permitted Mexico City residents to take cover or flee buildings. The earthquake was not serious but there is consensus that it worked. The attached video shows a local Mexico City TV announcer's reaction to the earthquake. In the background you can hear the early warning sirens.