Mexico City was rocked Tuesday afternoon by a 7.1-magnitude earthquake that collapsed buildings, damaged roads and killed scores of people — 32 years to the day that another quake in 1985 devastated the city and left thousands dead.

Earthquakes from Sept. 4-19

Merida

MEXICO

200 MILES

Gulf

of

Mexico

Mexico City

Veracruz

Puebla

Tuxla

Gutierrez

Magnitude 7.1

Sept. 19

GUATEMALA

Over 200 earthquakes

with magnitudes

between 4 and 5.6

Guatemala

City

Magnitude 8.1

Sept.8

Fault

Merida

200 MILES

MEXICO

Gulf

of

Mexico

Mexico City

Veracruz

Puebla

Belmopan

BEL.

Acapulco

Tuxla

Gutierrez

Magnitude 7.1

Sept. 19

GUATEMALA

HOND.

Guatemala

City

Over 200 earthquakes

with magnitudes

between 4 and 5.6

El SAL.

Magnitude 8.1

Sept.8

San Salvador

Size of the circles represent the energy released by each earthquake, not the magnitude. A magnitude-8 earthquake can release about a million times more energy than a magnitude 4, not twice as much, since the magnitude scale is logarithmic.

In seismically active regions like much of Mexico, strong earthquakes are often followed or preceded by many smaller tremors. But this event is somewhat unusual in that it closely follows but seems unlikely to be related to an 8.1-magnitude quake, which occurred several hundred miles away less than two weeks earlier on Sept. 8.

Seismic events since Sept. 4,

by magnitude

Sept. 8

8.1 magnitude

8

7

Sept. 19

7.1 magnitude

6

5

4

3

2

1

0

Note: chart only includes events of

magnitude 4 or greater.

Seismic events since Sept. 4, by magnitude

Sept. 8

8.1 magnitude

8

Sept. 19

7.1 magnitude

7

6

5

4

3

2

1

0

Sept. 4

Sept. 8

Sept. 19

Note: chart only includes events of magnitude 4 or greater.

The country saw at least 206 seismic events of magnitude 4 or greater in the two weeks leading up to Tuesday’s earthquake, many of which seemed to be aftershocks of the larger Sept. 8 event, which occurred south of Mexico’s Pacific coast near the border with Guatemala.

Perceived shaking of Mexico’s two recent major quakes

Sept. 8

Merida

MEXICO

200 MILES

Gulf

of

Mexico

Mexico City

Veracruz

Puebla

Tuxla

Gutierrez

GUATEMALA

Epicenter

Perceived shaking

Guatemala

City

Moderate

Severe

Sept. 19

MEXICO

Gulf

of

Mexico

Mexico City

Puebla

Epicenter

GUATEMALA

Detail

Sept. 8

Merida

200 MILES

MEXICO

Gulf

of

Mexico

Mexico City

Veracruz

Puebla

Belmopan

BEL.

Acapulco

Tuxla

Gutierrez

GUATEMALA

Epicenter

HOND.

Guatemala

City

Perceived shaking

8.1 magnitude

El SAL.

Moderate

Severe

San Salvador

Sept. 19

Merida

MEXICO

Gulf

of

Mexico

Mexico City

Veracruz

Puebla

Epicenter

7.1 magnitude

 

Belmopan

BEL.

Acapulco

Tuxla

Gutierrez

GUATEMALA

HOND.

Atlantic

Ocean

Guatemala

City

Pacific

Ocean

El SAL.

Detail

San Salvador

Sept. 19

Sept. 8

Merida

Merida

200 MILES

MEXICO

MEXICO

Gulf

of

Mexico

Gulf

of

Mexico

Mexico City

Mexico City

Veracruz

Veracruz

Puebla

Puebla

Epicenter

7.1 magnitude

 

Belmopan

Belmopan

BEL.

BEL.

Acapulco

Acapulco

Tuxla

Gutierrez

Tuxla

Gutierrez

GUATEMALA

GUATEMALA

Epicenter

HOND.

HOND.

Atlantic

Ocean

Perceived shaking

Guatemala

City

Guatemala

City

8.1 magnitude

Pacific

Ocean

El SAL.

El SAL.

Moderate

Severe

Detail

San Salvador

San Salvador

The two epicenters were several hundred miles apart, but many areas felt moderate to severe shaking in both earthquakes. The Sept. 8 magnitude-8.1 quake was roughly 10 times stronger, but Tuesday’s earthquake was located closer to more heavily populated areas, mainly Mexico City and the surrounding states of Puebla and Morelos.

Tuesday’s quake was also closer to the surface — 31 miles down, compared to 43 miles down — than the Sept. 8 quake. Shallower quakes cause more shaking at the surface than deeper ones of the same magnitude because seismic waves lose energy as they travel.

A view of Mexico City after the earthquake. (Edgar Cabalceta/European Pressphoto Agency/EFE)

Chiqui Esteban and Armand Emamdjomeh contributed to this report.

Correction (Sept. 20): A previous version of this story incorrectly stated that the Sept. 19 earthquake happened 22 years to the day of Mexico’s devastating 1985 earthquake. It happened 32 years to the day.

About this story

Data of earthquake locations, magnitude, and perceived shaking from U.S. Geological Survey. The conversion from magnitude to energy released on the top map is based on a formula published by the Wichita State University Department of Mathematics, Statistics and Physics. The graphic shows energy as converted from the Richter scale instead of moment magnitude (used by USGS), but the differences at the level shown are not appreciable.

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