Minor Earthquake Activities

　　Sometimes, days or hours before the happening of a major earthquake, a series of small earthquakes may happen. The seismologists call such earthquakes foreshocks.

　　There are many such records in the historical earthquake materials in our country. For example, in 1512, “minor earthquakes happened successively for 13 days in Yunnan in May, then, a great earthquake happened in August”. 

　　Since there are a series of small earthquakes before a major earthquake, people can make use of such opportunities to forecast major earthquakes and to take measures to keep away with major earthquakes. In August 11, 1809, in Zhengan of Guizhou “the mountain shook suddenly and rocks started to roll down. The inhabitants took their draught animals to the opposite mountains because of this. Soon after that, the earth began to shake violently. Houses collapsed and the earth in the fields was even turned over. A pond was formed nearby a spring, which was as deep as hundreds of feet.” This illustrated that, before the major earthquake, the local people got to know the foreshocks and took effective measures,  so avoided heavy losses of property and life.

　　Sometimes, after a major earthquake, a series of small earthquakes also happen. These earthquakes are called aftershocks. People should also pay attention to such aftershocks.

　　If we could observe foreshocks, we could foretell a major earthquake. It also has great significance for people to carry out studies in earthquake forecast.