Why are earthquakes difficult to predict?

Mainly because of the complexity of seismic physical process.

Earthquakes are natural phenomena that occur in an extremely complex geological environment. The appearance of earthquake precursors, the geological environment in the focal area and the earthquake process are extremely complicated and changeable. This is a nonlinear process, and the linear process is very easy to handle. Once nonlinearity is involved, the difficulty of processing increases sharply.

Earthquake, also known as ground motion and ground vibration, is a natural phenomenon caused by the rapid release of crustal energy, and seismic waves will be produced in the process. On the earth, plates collide with each other, resulting in dislocation and rupture at the edge and inside of plates, which is the main reason for earthquakes.