The difference between earthquake early warning and forecast

- Jun 18, 2019-

People's Daily Online, Beijing, June 18 (Reporter Wei Yan) At 2:55 on June 17, a magnitude 6.0 earthquake occurred in Changning County, Yibin City, Sichuan Province. Many Sichuan netizens said that the relevant departments have successfully warned the earthquake and issued warnings to the public through outdoor broadcasting.


What is earthquake warning? How big is the earthquake warning effect? Professor Luo Qifeng, a professor at the Institute of Structural Theory at Tongji University, and related seismologists answered this question.


Q: What is an earthquake warning?


A: Earthquake early warning is not an earthquake prediction or forecast. Earthquake early warning refers to the time to win early warning based on the time difference between the longitudinal and transverse waves and the “race” of the seismic wave after the earthquake.


At the beginning of the earthquake, the faster-running longitudinal waves are about 7 km per second, and the more destructive transverse waves are delayed by tens of seconds due to the relatively slow propagation speed (about 4 km per second). Arrive at the surface. The deep underground detection instrument detects the longitudinal wave and transmits it to the computer, and immediately calculates the approximate information such as magnitude, intensity, and source. The relevant departments can rush to send an alarm through TV and radio 10 seconds before the transverse wave reaches the ground. Television broadcasting relies on electromagnetic waves, which are much faster than the shear wave speed. The effective operation of the early warning system relies on a strong seismic monitoring network.


Q: What is the difference between earthquake warning and earthquake prediction?


Earthquake prediction is to notify the earthquake event that has not yet occurred but is likely to occur. The earthquake warning is that a destructive earthquake has occurred and warned before the serious disaster occurs. Earthquake prediction is still a major problem worldwide, but earthquake warning is completely feasible.


Q: What is the effect of the earthquake warning system?


A: The principle of the early warning system determines that the emergency time it provides is limited. During this time, we can stop high-speed trains, evacuate from elevators, terminate or protect critical equipment and equipment, evacuate personnel to safe areas, and so on. But the role of early warning cannot be overstated.


This also reflects the law of the early warning system: the closer to the epicenter, the shorter the time to provide early warning; the farther away from the epicenter, the longer the warning time provided, but the significance is also weakened. In addition, because of the “fast” earthquake warning, the judgment of the magnitude of the earthquake, the source and other information may not be completely accurate. Therefore, the academic community still disagrees with the earthquake warning. The supporters believe that it can effectively avoid losses. The opponents believe that it requires long-term human and material input, but the effect is limited. In the long run, strengthening the seismic design of houses is a more effective way to resist earthquakes.