Mexico City Earthquake: Warning Awakens Residents as Aftershock Strikes Coast
Nick Wiltgen Published: Aug 26, 2013,
A man tries to salvage some belongings near his badly damaged home in Acapulco after a 5.3 magnitude aftershock which was reported minutes after a 6.2 magnitude earthquake shook Mexico City on Aug. 21, 2013. (Pedro Pardo/AFP/Getty Images)
Smartphone alarms of an earthquake warning Monday morning roused Mexico City residents from bed for the second time in less than a week, but the earthquake that triggered the warning proved to be relatively harmless this time.
The tremor, rated magnitude 4.4 by the U.S. Geological Survey and 4.8 by Mexico's National Seismological Service, was centered 29 miles east of Acapulco, near the town of San Marcos in the state of Guerrero. It appeared to be an aftershock of the magnitude-6.2 jolt that rocked the same area five days earlier on the morning of Aug. 21, causing damage to a number of buildings in Acapulco.
Monday's quake, which happened at 7:54 a.m. CDT, prompted an earthquake warning to be issued for Mexico City, waking countless residents in Mexico's capital city just as similar alarms had done for the Aug. 21 quake.
"Nothing like going out in pajamas and having joggers look at you strangely," one Twitter user in Mexico City wrote, adding, "This earthquake warning works pretty well."
Mexico City's earthquake warning system relies on a network of sensors that detect earthquakes in the seismically active zone along its Pacific Coast. Since electronic signals travel at 186,000 miles per second, much faster than the 7,000-mph speed of seismic waves, warnings can be sounded in Mexico City, some 150 to 200 miles away, with a minute or two of advance warning before those seismic waves arrive to cause shaking in the capital.
Mexico City's worst modern earthquake, a magnitude-8.1 temblor in 1985, originated in this coastal zone. As the capital is built on the sediments of a drained lake bed, it is vulnerable to significant shaking even from such relatively distant earthquakes.
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