Unit 5: The Dynamic Earth Chapter 19: Earthquakes     Predicting Earthquakes On February 4, 1975, an earthquake with a magnitude of 7.3 struck the Chinese city of Haicheng. The city was leveled, but only about 1300 people were killed. On July 28, 1976, another strong earthquake hit China. It had a magnitude of 7.6 and occurred near Tangshan. This city was also leveled. But unlike in Haicheng, the loss of life in Tangshan was substantial. At least 240,000 people died, and some estimates place the death toll at twice that figure. Why did the two earthquakes differ so greatly in the number of lives lost? Before exploring the question above, it would be helpful to know a bit about China's experience with earthquakes in general. China is an area under geologic pressure. It lies directly in the path of the Pacific plate, which is inching west, and the Indian plate, which is moving northeast. These tectonic forces create faults, and when faults reach the breaking point, earthquakes occur. China has thus been struck by numerous earthquakes throughout its history. Partly for this reason, the country has long been a forerunner in the field of earthquake prediction. The Chinese, for example, developed the first seismometer in the year A.D. 132, and have been recording the dates and relative strengths of earthquakes for more than 1000 years. During the 1960s, China was hit by several major earthquakes. In response, the government established "People's Stations," which were citizen groups responsible for monitoring impending signs of earthquake activity. Such signs are known as precursors. A typical precursor might be a series of foreshocks, or small tremors, that sometimes precede a major quake. The emission of radon gas from deep wells is another precursor, as are drastic changes in animal behavior—although it should be stressed that this sign is not considered reliable by many scientists. The People's Stations worked in conjunction with Chinese seismologists—both had the common goal of improving earthquake prediction methods. LINK UP: Find out more information about earthquake prediction. Success in Haicheng In the months leading up to the Haicheng earthquake, People's Stations in the region reported changes in water levels in wells, land elevation, and animal behavior. In addition, seismologists recorded a marked increase in foreshocks in the Haicheng area. A low-danger earthquake warning was issued. However, by early February, foreshock activity had risen to an alarming degree. Because most earthquake-related deaths occur when people are crushed by collapsing buildings, the residents of Haicheng were ordered to evacuate their homes. Thousands slept outside in makeshift huts in the cold February air. This action no doubt saved countless lives. Nine hours after the evacuation order, the earthquake hit. The prediction of this earthquake and the preventive actions taken were hailed around the world as a stunning success. Disaster in Tangshan One year later, however, Chinese seismologists were caught off guard when a devastating earthquake struck the city of Tangshan in the middle of the night. Most of the one million residents were asleep. Thus, the vast majority of the 240,000 victims were likely killed by falling rubble before they could rise from their beds. Only one road into the city remained open, and this was soon blocked by relief workers who inadvertently created an impassable traffic jam. The survivors were left without food, water, electricity, or medical aid for hours. They had scant shelter as well. More than 93 percent of all houses were destroyed. In terms of loss of life, Tangshan holds the record for the deadliest quake of the twentieth century. What went wrong? Why weren't the Chinese able to predict the disaster in Tangshan? Not all earthquakes are preceded by clear precursors. Some strike with little warning. At best, scientists can predict where an earthquake will likely occur, but not when. In the case of Tangshan, several precursors were noted after the earthquake had already hit. They were largely ignored because the area did not experience a marked increase in foreshock activity. The disaster in Tangshan underscores an important point about earthquake prediction—the field is still in its infancy. Even the Chinese, who correctly predicted the Haicheng quake, have far more failures than successes. Scientists are striving to make earthquake prediction as reliable as weather forecasting. In the meantime, however, a successful prediction is a rare event indeed. Activity A successful earthquake prediction can save countless lives. Form small discussion groups. Within each group, discuss additional reasons why earthquake prediction is useful. Share your results with other groups.