Masonry Magazine February 1986 Page. 24
Special Report
MEXICO
EARTHQUAKE
The major earthquake that rocked Mexico City and surroundings in September, 1985, was one of the worst disasters to hit the North American Continent.
Here is a special, two-part, eyewitness report prepared by the IMI investigative team that went to Mexico to assess the monumental damage and loss of lives.
The following is a pre-publication of a scientific document soon to be released by the International Masonry Institute describing the structural damage caused by the devastating earthquake that rocked Mexico in September, 1985. This is the first of two parts; Part II, which features a large number of photos taken by the IMI investigative team of actual damage caused by the earthquake, will appear in the March/April, 1986 issue of Masonry.
Voluminously illustrated, the entire document will be available for purchase at $2.50 per copy by contacting IMI at 823-15th St., Washington, DC 20005.
Masonry is deeply grateful to IMI for its permission to publish this special report as well as for its commitment and dedication to provide this scientific data for the better understanding and improvement of masonry construction in seismic areas.
INTRODUCTION
Background
At 7:17 a.m. (local time) on Thursday, September 19, 1985, a strong earthquake shook the western coast of Mexico, about 40 km (25 miles) offshore from the small town of Lazaro Cardenas. The earthquake focus was located by local instrument networks at 17.68° N, 102.47° W, at a depth of about 33 km. The earthquake's Richter magnitude (M) was first estimated at 7.8. and then upgraded to 8.1. It was followed by a strong (magnitude 7.5) aftershock at 7:38 p.m. the following Friday, September 20, 1985, and by many other smaller aftershocks in the following weeks.
Because the Mexican coast near the epicentral region is sparsely populated, damage there was not extensive. Due to the characteristics of the ground motion and the local geology, both of which are discussed later, the most severe effects of the earthquake were felt in Mexico City, about 400 km (250 miles) to the east-northeast of the epicenter. Mexico City has a population of approximately 18 million, of which about 8,000 persons lost their lives due to the earthquake, and another 10,000 were injured. More than 30,000 people lost their homes, places of employment, and possessions. There were about 800,000 buildings in the earthquake zone of the city. The areas where the most severe damage occurred are shown in Fig. 1.1. In a survey conducted soon after the quake, the Institute of Engineering at the National Autonomous University of Mexico (UNAM) identified 179 buildings which had collapsed, and an additional 85 buildings which were severely damaged and in danger of collapse. More than $5 billion in damage was suffered by the city, not including the long-term costs of rebuilding.
Because some initial reports described heavy damage to masonry buildings early in the week after the earthquake, the International Masonry Institute (IMI) organized a team of structural engineers to go to Mexico and evaluate the earthquake performance of all types of buildings, with particular emphasis on masonry. This report describes the findings of that team, and also provides other background information related to the earthquake.
The team was led by Robert J. Beiner, P.E., director of engineering for IMI, Washington, D.C. Other team members included James E. Amrhein, S.E., executive director, Masonry Institute of America, Los Angeles, Calif.: James C. Anderson. Ph.D., associate professor of civil engineering. University of Southern California; Richard E. Klingner, Ph.D., P.E., associate professor of civil engineering. University of Texas at Austin; Victor M. Robles, senior structural engineer, Office of the State Architect, Los Angeles, and Andrew Lautman, a professional architectural photographer from Washington, D.C.
The team met in Mexico City on the morning of
The devastation is almost indescribable in these collapsed sections of the Nuevo Leon housing structure at Tlatelolco, where hundreds of people perished amid the ruins. (Photo by Andrew Lautman)