On September 7, near Moxi Town, Luding County, Ganzi Prefecture, Sichuan Province, rescuers from the Chengdu Fire and Rescue Detachment in Sichuan Province transferred trapped people. Xinhua News Agency
At 12:52 on September 5, an earthquake of magnitude 6.8 occurred near Luding County, Ganzi Prefecture, Sichuan, with a focal depth of 16 kilometers. As of 14:00 on September 7, the earthquake had killed 74 people and lost contact with another 35 people. At present, the State Council Earthquake Relief Headquarters Office and the Emergency Management Department have raised the national earthquake emergency response level to Level 2, and various earthquake relief work is underway.
What are the similarities and differences between this earthquake and the Wenchuan earthquake 14 years ago? How about the aftershocks? Is there a connection with the climate anomaly mentioned by netizens? What improvements have been made in my country's earthquake early warning in the past ten years? "Science China" interviewed relevant experts.
One question: What are the similarities and differences with the Wenchuan earthquake geological background?
"The Luding earthquake, the fault zone and the way of earthquake movement are different from the Wenchuan earthquake 14 years ago." Xu Xiwei, president of the National Academy of Natural Disaster Prevention and Control, told the China Science Journal.
The Luding earthquake was located near the Moxi fault in the southeastern section of the Xianshuihe fault zone, and was a strike-slip type earthquake. The Wenchuan earthquake is located in the Longmenshan fault zone and is a thrust earthquake. "For example, the Wenchuan earthquake is like the collision of two oncoming cars, and the front of one car flew to the roof of the other car; and the Luding earthquake is like two cars passing by, and the distance has changed. But the elevation has not changed." Xu Xiwei said.
Xu Xiwei said that the Xianshuihe fault zone is located in a high mountain canyon. The Gongga Mountain in the west is the highest uplifted place on the eastern edge of the Qinghai-Tibet Plateau, with an altitude of more than 7,500 meters. "In addition to the damage caused by earthquake shaking, secondary geological disasters such as landslides, collapses, and mudslides can easily be triggered during earthquakes, resulting in damage to houses and personal injury," he said.
Wang Tun, director of the Chengdu High-tech Disaster Reduction Research Institute, said that there are three major fault zones in Sichuan Province, namely the Songpan-Longmenshan fault zone, the Xianshuihe fault zone and the Anninghe-Zemuhe fault zone. The epicenter of the Luding earthquake was located near the intersection of the three major fault zones.
Although the fault zone is different, Wang Tun said that the Luding earthquake, like the 2008 Wenchuan earthquake, both occurred in a larger north-south seismic zone.
This earthquake zone is caused by the collision between the Indian plate and the Eurasian plate. It can extend to Mongolia in the north and India in the south. After passing through Ningxia, Gansu, Sichuan and Yunnan in my country, intermediate earthquakes of magnitude five or six, even seven or eight, often occur. magnitude earthquake. In recent years, earthquakes of magnitude 6 or above, such as the Ludian earthquake in Yunnan, the Jinggu earthquake and the Jiuzhaigou earthquake in Sichuan, all occurred here.
Second question: How about the aftershocks?
Is the Luding earthquake likely to trigger stronger aftershocks? Wang Tun believes that this possibility exists. At present, the degree of surface rupture caused by the Luding earthquake is about 30 kilometers, and the change of the in-situ stress energy beyond 30 kilometers is very small. There is still the possibility of a magnitude 7 earthquake. "The earthquake released part of the energy, and part of the energy to be released," he said.
Xu Xiwei also said that the China Earthquake Administration has believed for decades that there is a risk of an earthquake of magnitude 7 or greater here. He worries that the quake may be a foreshock of a larger one, triggering the main rupture of the southern Anninghe fault zone and the Daliangshan fault zone, which requires more research.
The China Earthquake Network is closely monitoring the local aftershocks. According to the latest news, as of 7:00 on September 7, a total of 13 aftershocks of magnitude 3.0 and above have been recorded, including 2 earthquakes of magnitude 4.0-4.9, 11 earthquakes of magnitude 3.0-3.9, and the largest aftershock is currently 4.5.
Three questions: Is there a correlation with climate anomalies?
On September 6, in order to assist post-disaster recovery and reconstruction, Sichuan Province terminated the four-level drought emergency response that began on July 15 due to continued high temperature and drought. In this regard, some supporters of the "drought earthquake theory" believe that drought may be a precursor to a major earthquake - the friction of the stratum before a major earthquake will cause heat, which will lead to increased surface temperature and drought.
Wang Tun believes that the scientific evidence is insufficient. "The dislocation of a large earthquake occurs about 10 kilometers underground, and even if the heat is transmitted to the surface, it will take a hundred years, a thousand years or more. It is impossible to associate drought with large earthquakes within a few years." He said, Wenchuan Before the earthquake, there was no drought in the whole province of Sichuan.
In addition, after the earthquake, the China Meteorological Administration issued a weather forecast saying that in the next three days, there will be more rain in Luding County. Some netizens said that meteorological disasters such as heavy rain or hail occurred after the Tangshan and Wenchuan earthquakes. Could this weather anomaly be related to atmospheric disturbances caused by exposure to chemicals released from the underground bedrock after the earthquake?
Wang Tun said in this regard that "accidental phenomena cannot be regarded as inevitable" and "pseudo-correlation" should not be carried out. "For example, the Lushan earthquake did not rupture on the surface, and the gas and chemical substances in the ground could not be released, but it also rained because it was facing the rainy season." He suggested that scientifically guide online public opinion and carry out earthquake prevention and disaster reduction work normally.
However, Xu Xiwei said that related research, such as some geochemical tracking and monitoring, is still needed to determine whether the heavy rain after a major earthquake is related to the changes in local climate conditions caused by the earthquake. Because such compound disasters and secondary disasters will increase the degree of damage, it is necessary to prevent the occurrence of meteorological disasters after major earthquakes as much as possible.
Fourth question: What is the progress of earthquake early warning and forecasting in my country?
In the face of the worldwide problem of earthquake prediction, Xu Xiwei said frankly that in the past ten years, through the combination of big data and artificial intelligence technology, earthquake prediction is changing from empirical prediction to physical prediction guided by models and theories. However, this aspect is still in the preliminary exploratory stage, and the level of earthquake monitoring and forecasting has not achieved the great progress expected by people.
"Like the Luding earthquake, we have already pushed forward the activity of the fault zone, but due to the lack of in-depth understanding of the earthquake mechanism and occurrence process, there are still challenges in earthquake prediction." He said that the theory, technology and practice of earthquake prediction are needed in the future. a substantial leap.
In order to prevent problems before they occur, Xu Xiwei said that a necessary basic work is to draw a map of the distribution of active faults across the country through large-scale mapping, "dig out" the source of earthquake disasters in the city, and try to "avoid" in urban development. He said that only about 160 active fault zones have been mapped so far, while there are more than 1,000 active fault zones in the country, and there is still a long way to go in this regard.
"Earthquake faults can dislocate rocks more than ten kilometers deep underground. The fault dislocation of houses on the surface is as easy as tearing a piece of paper." Xu Xiwei said that the current anti-seismic measures are still unable to prevent the damage of this dislocation nature, so try to avoid the source of the disaster.
In terms of earthquake early warning, a number of scientific teams have attempted to establish a "scientific test site for earthquake prediction" in the earthquake-prone Sichuan and Yunnan regions. Wang Tun said that since 2008, my country's related technologies have undergone subversive changes from scratch to leading the world; in the United Nations initiative from single disaster to multi-disaster early warning and even disaster chain early warning, my country's implementation efforts It is a global leader, with abundant channels for earthquake early warning and road traffic emergency response; in the future, it is still necessary to continue to improve and improve the existing emergency management mechanisms and measures.
(Original title "Four Questions about the Luding Earthquake Fault Zone and the Different Way of Earthquake Movement from the Wenchuan Earthquake")