What was a seismograph used for in China?

In ancient China, a seismograph was used to detect and measure earthquakes. The most famous early version, invented by Zhang Heng in 132 AD, featured a bronze vessel with eight dragon heads that would drop a ball into a corresponding receptacle when an earthquake occurred, indicating the direction of the quake. This device helped alert authorities to seismic activity, allowing for early warnings and response measures to protect communities. Its invention marked a significant advancement in the study of earthquakes and natural disasters in Chinese history.