The various precursors include the following.
- Fluctuations in water levels – The water table may change, resulting in changes in the water level in the wells. This is due to ground deformation. 3 to 10 days before the earthquake, the water level will fluctuate. For example, the 1975 HaiCheng earthquake caused a rise in water levels.
The high magnitude 7.3 1975 HaiCheng earthquake had a low death toll of 2041. This was because the earthquake was accurately predicted and the city of HaiCheng, of about 1 million, was evacuated. 4 days later, the earthquake struck, killing a small percentage of the city population.
However, prediction is limited.