China News Service, Beijing, July 12 (Reporter Sun Zifa) China Earthquake Networks Center held a briefing meeting on the Tangshan Guye M5.1 earthquake in the afternoon on the 12th to confirm that the 5.1 magnitude earthquake that occurred in Guye District, Tangshan City, Hebei Province that morning was 1976. An ups and downs activity of a magnitude 5 aftershock in the Tangshan M7.8 earthquake sequence in 2014.
The China Earthquake Networks Center held a briefing meeting on the Tangshan Guye M5.1 earthquake, and seismic experts answered questions. Photograph by Sun Zifa
It is unlikely that another magnitude 5 or more earthquake will occur in the short term
Researcher Liu Jie, deputy director of the China Earthquake Networks Center, said that the center organized experts to conduct a special study and analysis that the Tangshan Guye 5.1 earthquake occurred in the old earthquake area of the Tangshan M7.8 earthquake in July 1976. A normal earthquake fluctuation activity in the old earthquake area was also another aftershock of magnitude 5 or more after the Tangshan Guye M5.0 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.
Aftershock duration is related to tectonic loading rate
Why does a magnitude 5 aftershock occur more than 40 years after the Tangshan earthquake? Researcher Jiang Haikun, chief engineer of the Earthquake Prediction Department of the China Earthquake Networks Center, explained that the duration of aftershocks is related to many factors, the most important of which is the magnitude of the main shock. The larger the magnitude of the main shock, the longer the duration of the aftershock. However, the magnitudes of the main shocks are similar, and the duration of the aftershocks will also vary greatly. For example, the 2001 Kunlun Mountain Ms8.1 earthquake had aftershock activity of about half a year, and the Tangshan earthquake still had aftershock activity more than 40 years later.
He pointed out that according to preliminary research results, the duration of aftershock activity is actually related to the seismic tectonic loading rate. The faster the tectonic loading rate, the faster the aftershock attenuation. Compared with the eastern and western parts of mainland China, the geological tectonic loading rate in Tangshan is very slow, so The aftershocks of the Tangshan earthquake also lasted very long, and would last for hundreds of years. This is also a field of aftershock research that is currently generally accepted by the international scientific community.
Liu Jie added 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 has gestated for thousands of years. Hundreds of years is relatively normal."
332 aftershocks of magnitude 4 or above have occurred in the Tangshan old earthquake area
According to the China Earthquake Networks Center, as of now, there have been 332 aftershocks of magnitude 4 and above in the Tangshan 7.8 earthquake sequence in 1976, of which 300 were 4.0-4.9, 29 were 5.0-5.9, 2 were 6.0-6.9, and 7.0 were 1 time above. The magnitude 7 and above was the Luanxian 7.1 magnitude earthquake in Hebei on the day after the Tangshan earthquake that year.
The Tangshan 7.8 earthquake sequence activity is bounded by its last aftershock of magnitude 6 or above, and it can be divided into two stages so far: First, from the 1976 Tangshan earthquake to the May 1977 Tianjin Hangu earthquake of magnitude 6.2, a total of 5 occurred in the Tangshan earthquake area. There are 27 aftershocks above magnitude, with an average of 2.8 earthquakes of magnitude 5 or more in a month; second, since the 6.2 magnitude earthquake in 1977, the aftershocks of the Tangshan earthquake have been significantly attenuated, and only 5 aftershocks of magnitude 5 or more have occurred, with an average of 8.6 years 1 An earthquake of magnitude 5 or more. The Tangshan Guye magnitude 5.1 earthquake is about 25 years away from the last aftershock of magnitude 5 or above (October 6, 1995 Tangshan Guye magnitude 5.0 earthquake).
This earthquake will not have a significant impact on the seismicity of Beijing
Liu Jie pointed out that the aftershock area of the Tangshan earthquake has a long axis of 140 kilometers, covering Hebei, Tianjin and other places. Although the aftershock area activity will affect the capital circle, Beijing is not in the aftershock area.
According to an official response from the Beijing Earthquake Administration, the Tangshan Guye M5.1 earthquake caused a sensation in Beijing, among which Pinggu, Shunyi, Tongzhou and other regions in the east are more susceptible. The maximum seismic intensity recorded by the instrument is three degrees.
The Beijing Earthquake Administration stated that the epicenter of the earthquake was about 180 kilometers away from the center of Beijing. According to historical earthquake examples and physical model analysis, due to the long distance and small magnitude, this earthquake will not affect the stress, strain and earthquakes of Beijing’s crust. The activity has a significant impact. (Finish)