North China is one of the areas of strong earthquake activity on the Chinese mainland. Between the 1960s and 1970s, North China experienced the 1966 Xingtai Ms7.2, 1969 Bohai Ms7.4, 1975 Haicheng Ms7.3 and 1976 Tangshan Ms7.8 earthquakes, causing great losses of life and property. The Tangshan earthquake caused 240,000 casualties. In the past 50 years, Chinese seismologists have conducted large-scale deep geophysical exploration and research, obtained the detailed crustal and upper mantle structure, and revealed the deep tectonic environment of strong earthquakes in North China.