40 years ago today, September 21, 1985 (August 7, 1985 in the lunar calendar), a major earthquake occurred in Mexico and killed thousands of people. Densely populated Mexico City was damaged by an earthquake measuring 7.8 on the Richter scale. On September 21, 1985, rescue troops and people who lost loved ones used shovels, pickaxes, and even hand digging gravel and tiles in Mexico City to rescue victims of the earthquake. The earthquake occurred at 7:19 a.m.(9:19 p.m. Beijing time on September 21) and has been found to have killed thousands of people; a large number of buildings were destroyed and many more people were buried under reinforced concrete. All hospitals are saturated. 36 hours later, a severe aftershock occurred again. Everyone was panicked by the earthquake, and their families gathered on the streets to watch their homes be destroyed. One survivor said: "I heard a loud noise and grabbed my daughter and jumped out of the window. Before I could get out to save my wife, she was buried in the gravel and died. "This was a 7.8-magnitude earthquake on the Richter scale and was extremely destructive. The aftershock also had a magnitude of 7.3. Both geological epicenters were 230 miles south of Mexico City, but the one most affected was the capital, Mexico City. Many houses collapsed in the city center, including some high-rise buildings with more than ten stories. Several sections of the famous Avenue Juarez were in ruins. Fires were caused by ruptured gas pipes in some parts of the city. After the earthquake, traffic was interrupted in most parts of the city and all subways were suspended. Mexico City International Airport also announced a temporary closure. Water, electricity and gas were cut off in many urban areas, and local and long-distance calls were also cut off. Mexican President Meiger de La Madrid said the earthquake severely damaged 50 buildings, and more than 20 of them completely collapsed when the aftershock occurred. Tall piles of rubble have been turned into cemeteries, and rescue troops quickly disinfected some of them to prevent the spread of disease. According to radio reports here, the earthquake's epicenter was on the bottom of the Pacific Ocean about 400 kilometers southwest of Mexico City, affecting Mexico City and three states along the Mexican coast. Rescue workers are nervously searching for survivors in the ruins. This work carries many dangers, and usually only one can use your hands to open the bricks and soil to avoid injuring people. Masks are necessary, but what must be more vigilant is the extremely harmful aftershocks