Earthquakes in Mexico

The 1985 earthquake centered beneath Mexico City occurred when the Cocos Plate lying beneath the Pacific Ocean broke free from the North American Plate. The power of this magnitude 8.1 earthquake was incredible. Buildings shook in Texas, sloshed water out of pools in Colorado, and scientists say the entire planet vibrated like a bell being struck. When the shaking stopped, eighteen million people in Mexico City (one of the most populated urban areas on earth) began assessing damage. Thousands lay buried. In the Benito Jaurez Hospital alone, over one thousand propel died. A shift change of doctors, nurses, and staff was taking place just as  the hospital collapsed.

Remnants of the Benito Jaurez Hospital

A 7.6 aftershock occurred the next day. Seven-thousand buildings in Mexico City suffered complete destruction. Thirty-thousand people were injured, and ninety-five thousand were left homeless. It was Mexico's worst natural disaster in history. Reconstruction costs were reported to be more than four billion dollars. Downtown Mexico City is built on a foundation of soft sedimentary material, the remnants of an ancient lake bed. Mexico City lies over the remains of another city that once flourished. The Aztecs built their capitol, Tenochtitlan, upon this exact location. Lake bed sediments of sand and clay amplifies seismic waves, causing firm ground to become soft in a process called liquefaction.

The Mexico City earthquake actually occurred as two separate events twenty-six seconds apart. Unstable subsoil of sand, mud on top of clay, and gravel are all held in a bowl of bedrock. This geologic combination is so soft that ordinarily, buildings in Mexico City can sink as much as 6 inches every year. During the earthquake, buildings swayed for over three minutes. The last major quake to rock this area was in 1957.  A tent city was put up after the quake that housed 100,000 people.

Excellent construction techniques used by the Aztec's was demonstrated during this earthquake. Both the Metropolitan Cathedral, built by the Aztecs in 1525 AD, and the National Palace, built around 1700, remained standing. Neither suffered severe damage from this major earthquake, even though modern buildings on the same block fell into complete collapse.
 Just forty miles southeast of Mexico City (the world's largest metropolitan area of 20 million people) lies the 17,991 foot high peak of Popocatepetl. It is Mexico's second highest peak. Since 1922 the volcanic mountain has been relatively quiet. In recent times, scientists have documented increased gas emissions and seismic activity from the mountain. The increase in activity has been enough to cause the Mexican Government to examine evacuation plans for towns closest to the mountain. 

Not only is Mexico City located very near the volcano, but the town of Amecameca, population 25,000, and Puebla, population two million, lie at its very base. 

In the first months of 1994, researchers determined that this volcano was ejecting 1,320 tons of sulphur dioxide into the atmosphere every day, making it one of the six most active volcanoes in the world. It has previously erupted at least 25 times over the past 600 years. In 1665, the town of Puebla was completely covered in ash.  Before the Spaniards arrived, the Aztecs worshipped Popocatepetl as "Smoking Mountain", connecting it with legends of a great warrior. 

In 1521 five Spanish conquistadors hiked to the summit crater and excavated a load of sulphur because they had run out of gunpowder. The mountain has never had a significant eruption in recorded history. It showed signs of major activity last from 1920 to 1922. 

Guatemala
Guatemala experienced a major earthquake in 1976 that killed over twenty-three thousand people. South America's greatest earthquake activity occurs beneath Chile and Peru. In this century, twenty-three earthquakes with magnitudes over 7.5 have occurred in Central and South America. 

Chile
The strongest earthquake magnitude ever recorded in history occurred just off the coast of Chile in 1960. This incredible tremor had a magnitude of 9.5.

Damage from the 1960 Chile earthquake, the largest recorded earthquake in history.

Columbia
Prior to the eruption of Mt. Ruiz in Colombia in 1985, scientists noted a larger volume of escaping gasses than normal. Seismographs registered numerous strong tremors. Fresh ash was found on the top of the snow covered ground. Months later a volcanic tremor lasted three full days. People living in the village noticed a strong sulphur smell. After over four-hundred years of dormancy, hot ash, gas, molten material and rocks (called pyroclastic flow) ejected from the volcano in a great explosion.