On Thursday September 19, 1985 at 7:19 A.M., an earthquake jolted a large part of Mexico, causing enormous material damage and great loss of life in Mexico City and several other local towns. This quake, with a magnitude of 8.1 on the Richter scale, had its epicenter about 240 miles from the capital. On the following day at 7:30 P.M. an aftershock of 7.5 magnitude caused added damage and great alarm among the residents of Mexico City. The Mexican Cement and Concrete Institute (IMCYC) responded immediately to official requests and with a group of 19 engineers and architects from its staff participated with vehicles and equipment in a visual inspection coordinated by the Secretary of Urban Development and Ecology.
This is the strongest earthquake that has ever affected such a great concentration of population. The peculiar characteristics of the seismic movement and the dynamic response of the soils and the structures call for a general review of our construction technology and building codes, as well as the creation of methods for stricter supervision and quality control in construction. There were some 20 sustained cycles with a dominant period of vibration of 2 seconds. Those structures whose natural period of vibration was 2 seconds or a little less entered into resonance with the earthquake and suffered substantial damage or total collapse.
TYPES OF DAMAGE AND COMMON ERRORS DEDUCED FROM OBSERVATION
Many of the observed structural failures were caused primarily by human errors of the following type:
- Errors in design
- Change of use
- Building alterations
- Foundation failures
- Poor quality or deterioration of materials
- Errors of execution and lack of supervision.