The violence of the quake hurled people 2m (6ft) into the air, and within a matter of seconds 95 per cent of Tang-shan had collapsed into rubble. The earth split open into wide fissures and thousands of sink-holes, trees were uprooted and railroad tracks buckled. Amazingly, coal-miners working in the solid rock deep below Tang-shan survived the violent shaking that razed the city above them.
Source: wiktionary