Interpretation of News｜Expert Interpretation: Why did the Tangshan earthquake 44 years ago still have aftershocks?
At 6:38 on July 12, an earthquake of magnitude 5.1 occurred in Guye District, Tangshan, Hebei (39.78 degrees north latitude, 118.44 degrees east longitude), with a focal depth of 10 kilometers. On the same day, the Tangshan Emergency Management Bureau responded that the earthquake was a aftershock of the 1976 Tangshan earthquake.
Why did a large earthquake of magnitude 7.8 44 years ago still produce aftershocks? On the afternoon of the 12th, an earthquake expert from the China Earthquake Administration told Peng Pai News (www.thepaper.cn) that according to the aftershocks, the Guye District was located on the rupture zone of the original Tangshan earthquake and had a magnitude smaller than that of the main shock of the year. This 5.1-magnitude earthquake belongs to "the strong long-term aftershock of the 1976 Tangshan earthquake".
According to the aforementioned earthquake experts, the judgment of aftershocks mainly depends on whether the epicentral area occurred in the seismic zone of the original earthquake, and the magnitude is smaller than that of the main earthquake. Generally speaking, earthquakes that occurred in the original seismic zone after 40 to 50 years or even 60 to 70 years are considered "long-term aftershocks." Some seismologists in the world believe that the long-term aftershocks of some major earthquakes may last more than 100 years.
He explained that because after a large earthquake occurs, it will cause a fairly long rupture zone. The adjustment of the stress and strain of this rupture zone will last for a long time. During the adjustment process, many small ruptures will occur, and a lot of extraneous earthquakes will occur. . There were many aftershocks in the Xingtai earthquake in Hebei in 1966, the Haicheng earthquake in Liaoning in 1975, the Tangshan earthquake in 1976, and the Wenchuan earthquake in 2008. Earthquakes that are far away from the main shock are called long-term aftershocks. Some long-term aftershocks have smaller magnitudes, magnitudes 2 and 3 are even smaller, but some large aftershocks also occur, reaching magnitudes 4 and 5 and above. The Tangshan Guye earthquake happened on the rupture zone of the Tangshan earthquake, so it can be judged as the aftershock of the Tangshan earthquake.
According to the progress of the expert, the 5.1 magnitude earthquake in Guye District is the largest aftershock in Tangshan in recent years. To be precise, this aftershock should be called "long-term strong aftershock of the 1976 Tangshan earthquake". There will be aftershocks in the Tangshan earthquake zone in the future, but long-term aftershocks will become smaller and smaller. However, it cannot be ruled out that some large long-term aftershocks will occur in the aftershock area of Tangshan in the future, such as aftershocks of magnitude 4 or even magnitude 5.
According to the China Earthquake Networks News on the 12th, there have been 24 earthquakes of magnitude 3 and above in Hebei in the past five years. The largest earthquake is this one.
According to a report by Jin Yun on the 12th, the Guye earthquake was about 49 kilometers away from the Ninghe District of Tianjin City, which is generally felt in Tianjin. Tan Yipei, senior engineer of the Earthquake Monitoring and Forecasting Center of the Tianjin Earthquake Administration, said that the Guye District of Tangshan had previously had a magnitude 5.0 earthquake on October 6, 1995. From the periphery of Tianjin, Wen'an County, Hebei Province, had an earthquake in 2006. 5.1 magnitude earthquake. The earthquake occurred in the aftershock area of the Tangshan M7.8 earthquake in 1976, which was a normal seismic fluctuation activity in the Tangshan area.
The Beijing Municipal Earthquake Administration official microblog released news at noon on the 12th that the seismic activity in the aftershock area of the Tangshan earthquake was very rich, showing a state of fluctuation and attenuation. So far, there are still about 4, 5 earthquakes. According to expert consultation and analysis, it is unlikely that an earthquake of magnitude 5 or more will occur in the original area of the earthquake in recent days.
After the earthquake in Guye District, the Hebei Earthquake Administration and the Tianjin Earthquake Administration sent teams to the earthquake area to carry out emergency response work. The Ministry of Emergency Management initiates a four-level emergency response to earthquake disasters, and the Hebei Provincial People's Government initiates a three-level emergency response.
According to another report from China News Network, on the afternoon of July 12, the China Earthquake Networks Center held a briefing meeting on the Tangshan Guye M5.1 earthquake. Researcher Liu Jie, deputy director of the center, said at the meeting that, after expert discussion and analysis, the Guye earthquake occurred in the old earthquake zone of the Tangshan M7.8 earthquake in July 1976, which was a normal earthquake in the old earthquake zone of the Tangshan earthquake The ups and downs are another aftershock of magnitude 5 or more after the Tangshan Guye Ms5.0 earthquake in October 1995.
Liu Jie emphasized that according to the current observation data and analysis of earthquake cases, it is unlikely that an earthquake of magnitude 5 or more will occur again in the Tangshan old earthquake area in the short term. He also said that according to research in the world, the duration of aftershock activity is generally about 10% of the mainshock tectonic loading activity, that is, the mainshock gestation time, and the Tangshan earthquake lasted thousands of years. One hundred years is relatively normal."
Surging News noted that as early as March 12, 2010, the China Earthquake Administration had interpreted the recent earthquake situation for the public and introduced related knowledge, and mentioned the "Tangshan aftershocks" and "how to define aftershocks". When answering a reporter’s question, Liu Jie said that after a large earthquake occurred, a significant increase in seismic activity would be observed in its source area and adjacent areas. These obviously increased earthquakes are generally called aftershocks. There is currently no effective scientific method to clearly identify whether an earthquake is the aftershock of a major earthquake or another new earthquake.
Surging News Reporter Liao Yan