In the face of earthquakes, science is still promising. Through the study of seismic waves, it is found that seismic waves include P-waves and S-waves. The former propagates faster but has less destructive power, while the latter is the opposite. Therefore, through the seismic monitoring network, people monitor the P-waves of seismic waves with faster propagation speed and send signals to the monitoring center, The monitoring center can send an alarm to the public and key facilities by radio waves through the client. In other words, the earthquake alarm is a race between radio waves and seismic shear waves, which can warn people when the seismic shear waves have not yet arrived.
The scientific use of the time difference between two kinds of seismic waves can send out effective earthquake alarm is intended to explain that.