2017 Puebla earthquake

Date: September 19, 2017

Place: Puebla, Morelos, and Mexico City, Mexico

Result: about 370 dead, more than 6,000 injured

Overview

The 2017 Puebla earthquake, or Puebla-Morelos quake, occurred during a period of increased seismic activity in Mexico. Only twelve days before, on September 7, 2017, a devastating 8.2 earthquake located about 400 miles (650 kilometers) south of the Puebla epicenter had damaged the region of Chiapas, Mexico, killing 98. The 2017 Puebla quake struck on the thirty-second anniversary of a 1985 Mexico City earthquake that resulted in more than 10,000 deaths and $4.2 billion in damage. In fact, national commemorations of the 1985 disaster had taken place in Mexico City only hours before the 2017 earthquake.

As Mexico sits on one of the most seismically active areas in the world, seismological and global positioning sensors have been placed throughout the country to help measure seismic events and potentially predict future quakes. Researchers analyzing the data from these instruments discovered that the 2017 Puebla event was not only unrelated to either the 2017 Chiapas or the 1985 Mexico City quakes, but that it was the result of a highly unusual seismic activity. Typically, Mexican earthquakes are more likely to occur near the country’s Pacific coast where the Cocos plate that runs almost directly along Mexico’s west coast intersects with the North American plate that stretches across the nation’s southern border. The 2017 Puebla quake occurred in Mexico’s interior in an area 70 miles (112 kilometers) south of Mexico City. Such events are rare; since 1920, only five other such earthquakes have been recorded.

Typically, most earthquakes are the result of Earth’s tectonic plates rubbing against each other. When one plate slides against another during these movements, an earthquake occurs. However, the 2017 Puebla quake was the result of unusual movements of these plates. Initially, one of the plates stretching along an area of about 125 miles (200 kilometers) began sliding under its neighbor in a manner consistent with most earthquakes. Just as the plate began this movement, the rear of the plate suddenly shifted upward so that it was no longer moving diagonally under the first plate. Instead, it reoriented itself so that it bent straight upwards so that it sat horizontally beneath the portion of the North American plate upon which Mexico sits. Once shifted into this new position, the second plate suddenly moved again, this time directly downwards further into the Earth’s mantle from an area 30 miles (48 kilometers) where the initial plate interactions began.

Like a piece of wood being snapped in the middle, the dense rocks of the plates snapped, resulting in an earthquake. Earthquakes in which the plate moves downward in this manner are described as “bending.” The epicenters of such quakes occur near where the tectonic plate snaps. Usually, such earthquakes are less powerful than traditional subduction quakes in which one tectonic plate slips beneath another. However, bending earthquakes can still be quite powerful. The concern about these earthquakes is that since they occur inland, they are more likely to strike near Mexico’s large population centers like Mexico City.

Even worse, Mexico City was built over a dry lakebed. The soil in this area is mostly composed of silt, sand, and clay rather than hard rock. As a result, earthquakes in Mexico City tend to be felt more strongly. The parts of Mexico’s fault lines that can cause bending earthquakes run from the Michoacán state on Mexico’s central Pacific coast to the Oaxaca state along the southern Pacific coast. However, severe bending earthquakes are more likely to occur in the Puebla and Oaxaca regions due to the nature of the ocean floor near these locations. In these areas, the seafloor terrain runs parallel to the fault lines, a set-up that is more likely to allow bent tectonic plates to create “snapping” motions that result in massive tectonic movements and stronger earthquakes. Some of these more dangerous fault lines run as close as 30 miles (48 kilometers) south of Mexico City—well within the range of future earthquakes that could potentially level the city.

Impact

The 2017 Puebla earthquake occurred in the early afternoon on September 19 and lasted for about twenty seconds. It was rated at 7.1 on the moment magnitude scale, a system of seismic measurement is similar to the Richter scale. The earthquake occurred about 32 miles (51 kilometers) below the Earth’s surface, which is a moderate depth for an earthquake. Though the epicenter was located nearer to the town of Axochiapan in the state of Morelos, the earthquake was named after the larger city of Puebla which was only 34 miles (55 kilometers) from the epicenter. The earthquake epicenter was only 75 miles (120 kilometers) from Mexico City, which is known for its susceptibility to earthquake damage. The Puebla metropolitan area had a population of about 3.5 million at the time of the quake, while the Mexico City region had a population of 21.5 million. The United States Geological Survey (USGS) estimated that given the enormous population of the region, as many as 30 million people were subjected to at least moderate shaking.

Mexico City’s notorious vulnerability to earthquakes and its large size led to the earthquake’s greatest losses of life, with 228 of the confirmed 370 fatalities occurring in the nation’s capital. The greatest number of deaths occurred when the Enrique Rebsamen School collapsed and killed at least twenty-one children and two adults. As school was in session at the time of the earthquake, it was full of both students and teachers. The state of Morelos saw another seventy-five deaths. Many buildings in the cities of Puebla and Mexico City collapsed. About 184,000 homes and 16,000 schools were ultimately found to have been damaged between the two September earthquakes.

In the aftermath of the disaster, Mexico accepted a $150 million catastrophe fund from the World Bank to help rebuild and accommodate survivors left homeless. The United Nations Children’s Fund (UNICEF) was among the aid groups that responded to the emergency. The group was responsible for providing more than 1,500 medical care professionals and another 1,450 mental health consultants to help people affected by the disaster.

Bibliography

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