Sichuan is a high incidence area of earthquakes in China. I believe many people are deeply impressed by some earthquakes that have occurred in Sichuan. For example, Wenchuan earthquake, Jiuzhaigou earthquake and Ya'an earthquake. Why is the Sichuan earthquake?
Causes of Sichuan earthquake
The reason of Sichuan earthquake is that Sichuan Province is located in the Himalayan seismic zone, also known as Sichuan seismic zone. Most of them are distributed in the west of 104 ° e, mainly concentrated in Xianshuihe seismic zone, Anninghe Zemuhe seismic zone, Jinshajiang seismic zone, Songpan Jiaochang seismic zone, Longmen Mountain Seismic Zone, Litang seismic zone, Muli Yanyuan seismic zone, Mingshan Mabian Zhaotong seismic zone, etc.
Earthquakes in Sichuan Province are mainly concentrated in the following seismic zones (regions)
(1) Xianshuihe seismic belt: starting from Ganzi County, passing through Luhuo, Daofu, Kangding and other counties to the south of Luding County, the whole belt is in Ganzi Tibetan Autonomous Prefecture, extending from northwest to Southeast, which is the most earthquake prone and strongest seismic belt in Sichuan Province. There have been eight earthquakes with m ≥ 7 and above in this seismic belt, and the largest one is the one with magnitude 73 / 4 between Kangding and Luding in 1786.
(2) Anning River Zemuhe seismic zone: it starts from Shimian County in the north, turns southeast through Mianning County and Xichang City in the south, and then passes through Puge county and Ningnan County to Qiaojia county of Yunnan Province, mainly in Liangshan Yi Autonomous Prefecture. There have been three earthquakes with M = 6 and m ≥ 7 in the belt. The two largest earthquakes are the 7.5 earthquake in the north of Xichang in 1536 and the 7.5 earthquake in Puge, Xichang in 1850. The latter caused more than 20000 deaths, which is the largest earthquake in Sichuan Province.
(3) Jinsha River seismic belt: in Ganzi Tibetan Autonomous Prefecture, the wind starts from dege County in the north along the east side of the Jinsha River, passes through Baiyu and Batang counties and ends in Derong County in the south, extending along the north-south direction. In the belt, the Batang earthquake with magnitude 7.285 in 1870 and the strong earthquake swarm with m s6.7 in 1989 occurred in the belt.
(4) Songpan Jiaochang seismic belt: it is mainly located in Aba Tibetan and Qiang Autonomous Prefecture, including Jiuzhaigou, Songpan, Pingwu and Jiaochang of Maoxian county. There have been four earthquakes with m ≥ 7.5 in the belt, the largest is Diexi earthquake with M = 7.5 in Maoxian County in 1933.
(5) Longmenshan seismic belt: from Qingchuan County, through Beichuan, Maoxian, Mianzhu, Wenchuan, Dujiangyan, Dayi, Baoxing and other counties and cities to the vicinity of Luding County, it is distributed in the Northeast southwest direction, roughly consistent with the Longmen Mountains. There have been five earthquakes with m s6.0-6.9 in the belt, and the largest earthquake is the 2008 Wenchuan MS8.0 Earthquake. On April 20, 2013, at 8:02 Beijing time, a strong earthquake of magnitude 7,0 occurred in Lushan County, Ya'an, which is the southern section of Longmenshan seismic belt.
(6) Litang seismic belt: it is mainly located in Litang County of Ganzi Tibetan Autonomous Prefecture, spreading northwest southeast. There was a Litang earthquake with M = 7.3 in 1948.
(7) Muli Yanyuan earthquake area. In Muli County and Yanyuan County of Liangshan Yi Autonomous Prefecture, it can extend southward to Ninglang County of Yunnan Province. There have been five earthquakes with M = 6.0-6.9 in the area, and the largest earthquake is the 1976 6.7 earthquake between Yanyuan and Ninglang.
(8) Mingshan Mabian Zhaotong seismic zone: it starts from Mingshan County in the north, passes through Ebian, Mabian, Leibo and other counties in the north, and reaches Yongshan, Daguan and other counties in Zhaotong City, Yunnan Province in the south. There are two earthquakes with m ≥ 7 and above in the belt, and the largest is Yongshan ms7.1 earthquake in 1974. What magnitude is the largest earthquake in Sichuan history?
What magnitude is the largest earthquake in Sichuan history?
According to Sogou encyclopedia, the 5 & middot; 12 Wenchuan earthquake occurred at 14:28:04, Beijing time (UTC + 8) on Monday, May 12, 2008. According to the data of the Seismological Bureau of the people's Republic of China, the surface wave magnitude of the earthquake is 8.0ms, the moment magnitude is 8.3mw (according to the data of the U.S. Geological Survey, the moment magnitude is 7.9mw), and the earthquake intensity is 11 degrees. The seismic waves of this earthquake have been confirmed to have circled the earth for six times. The earthquake affected more than half of China and many countries and regions in Asia, ranging from Liaoning in the north, Shanghai in the East, Hong Kong, Macao, Thailand and Vietnam in the south, and Pakistan in the West.
The 5 & middot; 12 Wenchuan earthquake was an 8.0 earthquake at 14:28:04 on May 12, 2008 (Monday, the eighth day of April of the year of the fifth rat in the lunar calendar). The epicenter of the earthquake was located at the junction of Yingxiu town and Xuankou Town, Wenchuan County, Sichuan Province (2.5km to the west of Yuzixi Great Wall (World Heritage site of the great wall of China, at the foot of lianhuaxin mountain in niumiangou), 103 & deg; 42 ° E and 31 & deg; n; The location of Wenchuan earthquake is 30.986 ゜ 026.25 & prime; 214.3162 & prime; 103.364 ゜ 276.60 & prime; 333.0260 & prime; E) as approved by the US Geological Survey.
The reason: the Indian Ocean plate moves northward at the speed of about 15cm per year, which makes the Eurasian plate under pressure and causes the rapid uplift of the Qinghai Tibet Plateau. Due to the influence of gravity, the eastern side of the Qinghai Tibet Plateau is gradually sinking along the Longmen Mountain, and is faced with the tenacious obstruction of Sichuan Basin, resulting in the long-term accumulation of tectonic stress energy. Finally, the pressure suddenly released from Beichuan to Yingxiu in Longmen Mountain. It caused thrust, dextral and compressional fault earthquakes. The Sichuan earthquake occurred in the brittle ductile transition zone of the crust. The focal depth is 10-20 km, which is close to the surface of the earth and lasts for a long time (about 2 minutes). Therefore, the earthquake is very destructive and has a strong impact.