In the M=7.1 Puebla, Mexico earthquake on September 19, which caused significant damage in Mexico City, the city’s earthquake early warning sirens went off approximately 12 seconds before the strongest ground shaking (See video below – sirens go off at the 37 second mark). While the onset of shaking appears to begin only a few seconds after the sirens, that should have been enough for people to take cover underneath tables or desks.
by Ryan Hubbard