Why was there no advance notice of the Sichuan earthquake?

After the 7.8-magnitude earthquake occurred in Wenchuan County, Sichuan, the question of "why the earthquake cannot be predicted before it occurs, but can be predicted after it occurs" has become the focus of public attention. In response to this question, researcher Ding Xueren, chief earthquake forecast expert of the Fujian Provincial Seismological Bureau, answered here today.

He said that it is difficult to predict an earthquake before it occurs, and earthquake prediction has become a recognized scientific problem in the world. Earthquake prediction is much more difficult than originally thought, and the progress of earthquake prediction is much slower than originally thought. It can be considered that the level of global earthquake prediction is still quite low so far.

This researcher analyzed that it is difficult to predict earthquakes before earthquakes, mainly because: First, the complexity of the earthquake physical process itself and the "inaccessibility" of the earth's interior. Earthquake is a natural phenomenon that occurs inside the earth. The occurrence of earthquake is also a complex seismic physical process. Because there are too many unknown factors in the earthquake breeding process, the state of the source before the earthquake and the fine structure of the earth's interior cannot be directly detected, and the process of crustal rupture is very unstable. Even if humans have high-level simulation experiments, they are far from reaching the real environmental conditions at the earthquake source. In fact, the rupture of extremely heterogeneous media on a scale of hundreds of kilometers in the earth's crust cannot be simulated.

Secondly, the gestation and occurrence of earthquakes are the accumulation and release of strains caused by the stress on rocks in the earth's crust. The physical process and source of strain accumulation are the result of the superposition and repeated action of many factors. At present, it is difficult to understand the interrelationship between their evolutionary processes. Furthermore, major earthquakes are small-probability events that are difficult to repeat and test. Most of the so-called precursor phenomena before an earthquake does not have a one-to-one correspondence with the actual earthquake, and there is some uncertainty.

Ding Xueren said that when an earthquake occurs, through the modern instrument observation and data processing system of the seismic station, the time of the earthquake can be determined quickly (currently within one minute in Fujian) and accurately , location and intensity. However, after a destructive earthquake or an influential earthquake occurs, it is generally necessary to determine the post-earthquake trend to determine whether a destructive earthquake is likely to occur in the short term. It should be said that the overall level of earthquake prediction at this stage is still very low, and there are still unexpected earthquake events. After all, earthquake prediction research is still being explored.