China is located between two major seismic zones in the world - the Pacific Rim Seismic Zone and the Eurasian Seismic Zone, and is extruded by the Pacific Plate, the Indian Plate and the Philippine Sea Plate. All provinces, autonomous regions and municipalities directly under the Central Government.

Since 1900, as many as 550,000 people have died in earthquakes in China, accounting for 53% of global earthquake deaths; since 1949, more than 100 destructive earthquakes have struck 22 provinces (autonomous regions and municipalities directly under the central government), including 14 provinces in the eastern region, killing more than 270,000 people, accounting for 54% of all disaster deaths in China. This accounts for 54% of the deaths in all types of disasters nationwide, with earthquakes affecting an area of more than 300,000 square kilometers and collapsing 7 million houses. The severity of earthquakes and other natural disasters constitutes one of the basic national conditions of China.

Earthquakes in China are mainly distributed in five regions: Taiwan, southwest China, northwest China, northwest China, southeast coastal areas and 23 seismic zones.

The seismic activity in China is mainly distributed in five regions on 23 seismic zones. These five regions are: ① Taiwan Province and its nearby waters; ② Southwest China, mainly Tibet, western Sichuan and central and western Yunnan; ③ Northwest China, mainly in Gansu's Hexi Corridor, Qinghai, Ningxia, and the northern and southern foothills of the Tianshan Mountains; ④ North China, mainly on both sides of the Taihang Mountains, the Fenwei River Valley, the Yinshan-Yanshan area, central Shandong and Bohai Bay; ⑤ Guangdong and Fujian on the southeast coast. Taiwan Province of China is located on the Pacific Rim seismic zone, Tibet, Xinjiang, Yunnan, Sichuan and Qinghai provinces and regions are located on the Himalayan-Mediterranean seismic zone, and other provinces and regions are on related seismic zones. The distribution of China's seismic zones is an important basis for the development of key monitoring and defense zones for earthquakes in China.

Pacific Rim Seismic Zone Ring of Fire

The distribution of earthquakes is regular. Earthquakes in the world are mainly concentrated in three major seismic zones, namely: the Pacific Rim Seismic Zone, the Eurasian Seismic Zone (Mediterranean-Himalayan Zone) and the Ridge Seismic Zone.

The Pacific Rim seismic zone is the most dominant seismic zone on Earth, which is distributed around the Pacific Ocean like a huge ring, southward along the eastern coast of the Pacific Ocean in North America in Alaska, through the headquarters of Canada, California and the western region of Mexico, to Colombia, Peru and Chile in South America, then turning westward from Chile, across the Pacific Ocean to reach the eastern border of Oceania, in the eastern waters of New Zealand Turning north, then through Peiji, Indonesia, the Philippines, our Taiwan Province, the Ryukyu Islands, the Japanese archipelago, the Thousand Islands, the Kamchatka Peninsula, the Aleutian Islands, and back to Alaska in the United States, circling the Pacific Ocean for a week, also separating the continent from the ocean, where about 80% of earthquakes occur on Earth. The former concentrates about more than 80% of the world's shallow source earthquakes (0-70 km), almost all of the medium source (70-300 km) and deep source (300-700 km) earthquakes.

Analysis of the causes of earthquakes in the Pacific Rim seismic zone

The sea level rise caused by global warming causes a balanced rise of the continental crust that loses ice cover and a balanced fall of the oceanic crust that increases the sea surface, forming a new round of balanced crustal movement. On the spherical surface, the oceanic crust declines and will squeeze the continental crust to contract, and the land-sea margin is a strong squeeze zone [2-4]. The Alpine-Himalayan seismic zone is almost orthogonal to the Pacific Rim seismic zone, and the sequence of earthquakes indicates the inevitable process of Earth's surface deformation, and the pattern can be found by historical earthquake records. The general rule is that north-south symmetry and east-west echoes. Rupture in one place creates the conditions for rupture in another place. The yellow-deficit intersection angle reaches a maximum of 23.5 degrees at the winter and summer solstices. At the winter solstice, the high point of the solar tide reaches a maximum during the day at the Tropic of Capricorn and becomes a minimum during the night, while the high point of the solar tide reaches a minimum during the day at the Tropic of Capricorn and becomes a maximum during the night, forming a north-south oscillation of the maximum tide with a half-day cycle. At the summer solstice, the high point of the solar tide reaches its maximum value at the Tropic of Cancer during the day and becomes minimum at night, and the high point of the solar tide reaches its minimum value at the Tropic of Capricorn during the day and becomes maximum at night, resulting in the maximum north-south oscillation of the tide in a half-day cycle. If the white equatorial angle of the moon also reaches a maximum of 28.6 degrees at this time, and the sun and the earth approximate to a line, the strongest tidal north-south oscillation will be formed. This is the reason why strong earthquakes tend to occur near the winter and summer solstices [5]. 26 December 2004, the Moon's declination angle was 27.9 degrees for the Sun-Moon high tide, providing strong tidal conditions for the Indonesian earthquake and tsunami; 22 June 2005, the Moon's declination angle was 28 degrees for the Moon's near-Earth tide, and 23 for the Sun-Moon high tide, with the best conditions for the north-south oscillation of the tides and the greatest chance of forming strong earthquakes.

The Kamchatka-Japan-Philippines Southwest-Northeast Effect Zone is part of the Pacific Rim Seismic Zone - the Western Pacific Seismic Zone, and the California earthquake and the Chilean earthquake both occurred in another part of the Pacific Rim Seismic Zone -East Pacific seismic zone. In the future, seismic activity in the Kamchatka-Japan-Philippines-Sumatra belt is likely to intensify. This will clear the way for large earthquakes in Sumatra and Japan.

Seismic Records of the Pacific Rim Seismic Zone

Going back in history, numerous strong earthquakes have occurred in the Pacific Rim Volcanic Seismic Zone. 8.9 on the Richter scale, which occurred in Chile on May 22, 1960, is the strongest earthquake ever measured in the world.

Japan is on the western edge of the Pacific Rim Volcanic Seismic Zone, and is like sitting in a chair that is constantly shaking, with upwards of 1,000 felt earthquakes per year. Since the turn of the century, there have been more than 50 earthquakes of magnitude 6 or greater on the Richter scale. The Great Kanto Earthquake of September 1, 1923 destroyed 73% of the houses in Tokyo and 96% of the buildings in Yokohama, and killed 140,000 people, making people still talk about it. On October 4 and 9, 1994, another 7.9 and 7.3 magnitude earthquakes occurred in Kushiro City, Hokkaido; on December 28, 1993, a 7.5 magnitude earthquake occurred off Aomori Prefecture in northern Honshu Island; and on January 17, 1995, a 7.2 magnitude earthquake occurred in Hanshin area. Thus, Japan deserves the title of "Volcano Earthquake Country".

Across the ocean from Japan, the west coast of the United States is on the east side of the Pacific Rim Volcanic Seismic Zone. In the western part of California, from Los Angeles to San Francisco to the Pacific Ocean, a San Andreas fault has developed, with a total length of more than 965 km, which is a world famous active fault, and most of the strong earthquakes in the United States occur here. Since this century, 14 earthquakes of magnitude 6 or more on the Richter scale have occurred along the west coast of the U.S., including the massive 8.6 magnitude earthquake that shocked the world in San Francisco on April 18, 1906. 3 strong earthquakes of magnitude 7.6, 6.7 and 6.6 have occurred in the Los Angeles area since 1990.

North China Seismic Zone

    The "North China Seismic Zone". It includes all or part of the provinces of Hebei, Henan, Shandong, Inner Mongolia, Shanxi, Shaanxi, Ningxia, Jiangsu, and Anhui. Among the five seismic zones, it ranks second in the country in terms of earthquake intensity and frequency after the "Qinghai-Tibet Plateau Seismic Zone". Since the metropolitan area is located in this region, it is of particular concern. According to statistics, there have been five documented earthquakes of magnitude 8 and 18 earthquakes of magnitude 7-7.9 in the region. Coupled with its location in a densely populated area of China with a concentration of large cities and a developed political and economic, cultural and transportation area, the threat of earthquake disasters is extremely serious.

The North China seismic region is divided into four seismic zones.

 (1) Tancheng-Yingkou seismic zone. It includes most or part of Liaoning, Hebei, Shandong and Jiangsu provinces from Suqian to Tieling. It is a belt of strong seismic activity in the eastern continental region of China. 8.5 magnitude earthquake in Tancheng, Shandong in 1668, 7.4 magnitude earthquake in Bohai in 1969, and 7.4 magnitude earthquake in Haicheng in 1974 occurred in this belt, and it is recorded that more than 60 earthquakes of 4.7 magnitude or higher occurred in this belt. Among them, there were 6 earthquakes of magnitude 7-7.9; 1 earthquake of magnitude 8 or above.

 (2) North China Plain Seismic Zone. The southern boundary is located roughly along the Xinxiang-Bengbu line, the northern boundary is located on the south side of Yanshan Mountain, the western boundary is located on the east side of Taihang Mountain, the eastern boundary is located on the western edge of the Lower Liaoning River-Liaodong Bay arguing trap, extending southward to the southeast of Tianjin, and the economic south east reaches the area of Suzhou. It is the most threatening earthquake zone in Beijing, Tianjin and Tang area. 8.0 magnitude earthquake in Sanhe, Hebei in 1679 and 7.8 magnitude earthquake in Tangshan in 1976 occurred in this zone. According to statistics, more than 140 earthquakes of magnitude 4.7 or higher have occurred in this zone. Among them, there were 5 earthquakes of magnitude 7-7.9; 1 earthquake of magnitude 8 or above.

 (3) Fenwei earthquake zone. It starts from Xuanhua-Huai'an Basin and Huailai-Yanqing Basin in Hebei in the north, and goes southward through Yangwon Basin, Weixian Basin, Datong Basin, Xin Ding Basin, Lingqiu Basin, Taiyuan Basin, Linfen Basin, Yuncheng Basin to Weihe Basin. It is another zone of strong seismic activity in eastern China. 8.0 magnitude earthquake in Hongdong, Shanxi in 1303 and 8.0 magnitude earthquake in Huaxian, Shaanxi in 1556 both occurred in this zone. 6.2 magnitude earthquake in Zhangbei in January 1998 was also in the vicinity of this zone. Since records began, there have been about 160 earthquakes of magnitude 4.7 or greater in this seismic zone. Among them, there were 7 earthquakes of magnitude 7-7.9; 2 earthquakes of magnitude 8 or higher.

 (4) Yinchuan-Hetao seismic zone. It is located in the western and northern part of the Loop from Yinchuan, Uda, Dengkou to the west of Hohhot. 8.0 magnitude earthquake in 1739 in Yinchuan, Ningxia occurred in this belt. 6.4 magnitude earthquake in Baotou, Inner Mongolia on May 3, 1996 also occurred in this belt. In this seismic zone, historical earthquakes were recorded since 849 A.D. Due to the lack of historical records, there are about 40 earthquakes of magnitude 4.7 or higher recorded in this zone according to available data. Among them, there are 9 earthquakes of magnitude 6-6.9; 1 earthquake of magnitude 8.

Qinghai-Tibet Plateau Seismic Zone

 The "Qinghai-Tibet Plateau Seismic Zone" includes the vast plateau area enclosed by the Hindu Kush Mountains, West Kunlun Mountains, Arjinshan, Qilian Mountains, Helan Mountains - Liupan Mountains, Longmen Mountains, Himalayas and the eastern flank of the Transverse Range. It involves all or part of Qinghai, Tibet, Xinjiang, Gansu, Ningxia, Sichuan and Yunnan, as well as parts of the former Soviet Union, Afghanistan, Pakistan, India, Bangladesh, Myanmar and Laos.

The local seismic zone is one of the largest in China and is also the area with the strongest seismic activity and frequent occurrence of major earthquakes. According to statistics, 9 earthquakes of magnitude 8 or above have occurred here; 78 earthquakes of magnitude 7-7.9 have occurred. All of them rank the highest in the country.

Southeast Coastal Seismic Zone

Distribution of the Southeast Coastal Seismic Zone in China: The Southeast Coastal Seismic Zone geographically includes mainly Fujian and Guangdong provinces and a small part of the neighboring Jiangxi and Guangxi. This seismic zone is controlled by the northeasterly active fractures of the New China System, which are roughly parallel to the coastline. In addition, some northeasterly active fractures also play a role in forming seismogenic conditions. This group of north-east active ruptures from east to west are: Changle-Zhaoan Rift Zone, Zhenghe-Hefeng Rift Zone, and Shaowu-Heyuan Rift Zone. There have been many destructive earthquakes along the fracture zone, such as the 1604 Quanzhou overseas earthquake of magnitude 8 and a series of strong earthquakes near Nan'ao along the Changle-Zhao'an fracture zone, the Huichang earthquake of magnitude 6.0 (1806), the Heyuan earthquake of magnitude 6.1 (1962) and the Xunwu earthquake of magnitude 5.8 (1987) along the Shaowu-Heyuan fracture zone, and the Zhenghe -The Haifeng Fault Zone has also experienced destructive earthquakes, but the overall intensity is relatively low.

North-South Seismic Zone

From Ningxia in China, through eastern Gansu, western Sichuan, and Yunnan, there is a dense belt of earthquakes running roughly north-south across mainland China, known as the North-South Seismic Zone of China. The belt extends northward to Mongolia and southward to Myanmar, where the 8.0 magnitude earthquake in Wenchuan, Sichuan on May 12, 2008 occurred.

Others

In addition, the "Xinjiang Seismic Zone" and "Taiwan Seismic Zone" are two seismic zones in China that have experienced magnitude 8 earthquakes. It is also well known that strong and destructive earthquakes occur here constantly. Since the earthquake zone in Xinjiang is generally sparsely populated and economically underdeveloped. Although strong earthquakes are more frequent and frequent, most of them occur in mountainous areas and cause much less damage to people and property than several earthquake zones in the east of China.

It is worth mentioning the "Southeast Coastal Outer Zone" of the "South China Seismic Zone", where there were earthquakes of magnitude 8.0 in Quanzhou, Fujian in 1604 and 7.5 in Qiongshan, Guangdong in 1605. However, no significant destructive earthquakes have occurred in the 300 years since then until now.

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