Mexico City Was Built on an Ancient Lake Bed. That Makes Earthquakes Much Worse.

Mexico City Was Built on an Ancient Lake Bed. That Makes Earthquakes Much Worse.
By DEREK WATKINS and
Area of ancientlake bed
Shock waves froma simulated earthquake
The earthquake that on Tuesday killed at least 145 people in Mexico City
and toppled dozens of buildings there was all the more destructive because of the city’s unusual position atop an ancient lake bed.
Strength of shaking in Mexico City
These actual readings confirm what the simulation shows: Tuesday’s earthquake
grew worse in the city as its waves moved through the ancient lake bed below.
During an earthquake, the looser sediments near the surface cause shock waves to slow down from about one
and a half miles per second to about 150 feet per second as they enter the valley.
The animation above, based on a model by Víctor Cruz-Atienza, a professor of geophysics at the National University
of Mexico, shows how the shock waves of a hypothetical earthquake near Mexico City would spread.
The map below, based on seismological readings taken at the National University of Mexico,
shows how violently the ground shook in Mexico City during Tuesday’s earthquake.