All earthquakes start with P waves. These P waves move fast, causing the ground to shake up and down, causing less damage. The next one is the S wave, which moves very slowly, causing the ground to shake back and forth, left and right, and destructive The early warning system measures the movement of the P wave along the ground to predict the impact of the S wave and then issues an alert. However, scientists working on such systems have found that people don't have much time, in fact, Prepare for the earthquake. To reach the above conclusions, the most important prerequisites to be supplemented are:. ["there are more than 5 million earthquakes on the earth every year, and most people don't feel it.", 'According to the records of major earthquakes over the years, most of the strong earthquakes occurred instantly at night, and it was impossible to organize effective defensive operations in a short time.', 'the bigger the earthquake, the shorter the interval between the P wave and the S wave, leaving less time for people to warn.', 'When a large earthquake occurs, people first feel ups and downs, and then there is a strong horizontal sway. This sway is caused by the S wave.']