Failure In Placement

While arguably numerous factors played a role in the devastation and destruction of Mexico City in the 1985 earthquake, two factors in particular caused the most damage, the first being Mexico City’s location. Nearly 30 million years ago, mountains and volcanoes created a basin (History.com, 2008), in which Lake Texcoco formed (John A. Martin & Associates, INC, 2009). As the Aztecs expanded their capital (now Mexico City) they slowly drained and filled in the lake forming a plateau. As a result, Mexico City now rests on soft sedimentary clay deposits and sand, susceptible to liquefaction. (John A. Martin & Associates, INC, 2009). Though the primary waves caused a considerable amount of damage, the aftershocks and secondary waves only intensified the destruction. These soft sedimentary clay deposits allowed seismic waves to amplify as they arrived, and shaking lasted for up to three minutes in some areas (History.com, 2008).
Another major contributing factor was poorly built structures, especially those over 6 stories. These buildings were susceptible to failure because many did not meet standard building codes. As the ground shook, these buildings had a tendency to sway side to side and cause destruction to surrounding buildings, which would not have been as severely damaged after the quake (John A. Martin & Associates, INC, 2009). Some of the other main causes of building failure included the following: “corner building failure (42%), collapse of intermediate floors (40%), collapse of upper floors (38%), `pounding:' (one building repeatedly striking another during earthquake vibrations) (15%), and foundation failure (13%)” (John A. Martin & Associates, INC, 2009). A combination of poor building materials and substandard building codes were to blame for the exceptionally high level of building failure.
After the dust settled and the damaged was assessed, a third of all buildings in Mexico City had been damaged; nearly 100,000 buildings had suffered serious damage, and another 3,000 had been completely destroyed (History.com, 2008). Estimates brought the death toll to nearly 10,000 people, with another 50,000 suffering some sort of injury (History, 2008). As reconstruction took place, improvements were made to construction materials and redesign (BBC, 2009). Prior to the 1985 earthquake, the Mexican Government had been allowing buildings to be constructed which failed to meet proper building codes. Today new building codes are in place and being enforced to prevent a similar disaster from happening in the future (John A. Martin & Associates, INC, 2009). It is impossible to say how much less damaging this earthquake would have been if all appropriate measures had been taken in the original construction of Mexico City. Some buildings in the 25km2 radius were hardly damaged at all except due to contact with surrounding inferior structures. However, regardless of the quality of the surface structures, the underlying problem still remains in the foundation and composition of the earth. Due to the soft soil and sandy deposits, amplification and liquefaction would be unavoidable.