ExpertsPreliminary Judgment on the Largest Earthquake in Beijing in 23 Years in Huairou: Normal Fluctuation

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 ExpertsPreliminary Judgment on the Largest Earthquake in Beijing in 23 Years in Huairou: Normal Fluctuation

According to the official determination of the China Seismological Network, an earthquake of M 3.0 occurred at 12:47 on April 14 in Huairou District, Beijing, with a focal depth of 19 km, a epicenter of 40.34 degrees in the north latitude and 116.39 degrees in the East longitude. According to the official micro-blog of Beijing Seismological Bureau, Huairou, Yanqing and Changping felt strong earthquakes, while individual citizens in other areas felt earthquakes. According to the monitoring of seismograph intensity of Beijing Seismological Bureau, the instrument intensity in Huairou District has the strongest seismic sense of three degrees, which is basically consistent with that of netizens.

Intensity distribution map of Huairou M 3.0 seismograph. Tuyuan: Official Weibo of Beijing Seismological Bureau

According to the China Seismological Network Center, this earthquake is the first one of magnitude 3.0 and above in Beijing since 1996.

Liu Guiping, deputy director of China Seismological Network Center, told reporters that the level of seismicity in Beijing in the past ten years is very low. This years M3.0 earthquake is the largest one in recent years. But before 2000, small earthquakes in Beijing area were relatively active, so this should be a normal fluctuation of seismicity, but more cases need to wait for the results of expert consultation before further explanation. At the same time, she pointed out that the Haidian M2.9 earthquake in Beijing on April 7 last week and the Huairou M3.0 earthquake should belong to natural earthquakes caused by normal tectonic activities.

Beijing is located in the Yanshan seismic belt, but the occurrence of large earthquakes in Beijing is a small probability event. It happens only once in several hundred years. Most of the time, the seismicity is still at a relatively low level. Liu Guiping said that the last earthquake with magnitude 5 or more around Beijing was a magnitude 5.1 earthquake in Wenan, Hebei Province, on July 4, 2006, when the earthquake was felt in Beijing. No earthquakes with magnitude 5 or above have occurred in Beijing for more than 200 years. Generally, the level of seismic activity in Beijing is relatively low, but there will be some small fluctuations in a period of time.

Reporters learned that the Yanshan Mountains is where the Yanshan seismic belt is located. Beijing is located in the transitional zone between the Yanshan uplift zone and the subsidence area of the North China Plain. Two groups of faults with NE and nearly E-W directions converge here, and the geological structure is complex. According to statistics, since 294 AD, there have been four earthquakes with magnitude 5.0 to 5.9, six earthquakes with magnitude 6.0 to 6.9 and one earthquake with magnitude 8 in Beijing. Among them, the largest earthquake was the Sanhe-Pinggu M8 earthquake in 1679.

China Seismic Intensity Classification Table and Reference Table of the Corresponding Relation between Magnitude and Intensity. Tuyuan: Official Weibo of Beijing Seismological Bureau

According to the catalogue of quick report of China Seismological Network, eight earthquakes with magnitude 3 or above occurred in the past five years within 200 km of the epicenter of the Huairou earthquake. The largest earthquake was the magnitude 4.3 earthquake (84 km from the epicenter) that occurred on September 6, 2014 in Zhuolu County, Zhangjiakou City, Hebei Province.

In addition, since the earthquake was only a week away from the last Haidian earthquake, some people have raised speculations about whether successive small earthquakes could predict large earthquakes. In response to this speculation, Liu Guiping explained that, as the saying goes, small earthquakes make big earthquakes, but most of them do not have large earthquakes after small earthquakes. There is no necessary connection between the two, only in some cases, but this situation is very rare. There will be aftershocks after large earthquakes, but the level of aftershocks varies, which is closely related to local geological conditions and is usually difficult to predict. The Huairou M3.0 earthquake in Beijing has a smaller magnitude. If it is an isolated earthquake, there may be no aftershocks. If it is a major aftershock, the magnitude difference of aftershocks is more than one degree under normal circumstances, and it is almost impossible to feel them when they reach magnitude 2 or 1.5. In terms of historical earthquakes, Beijing still accounts for a large proportion of isolated earthquakes on the whole.

Source: Yang Yi_NBJ10647, Responsible Editor of Beijing Newspaper