The Longmenshan Fault () is a

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

which runs along the base of the

Longmen Mountains The Longmen Mountains (), also tautologically referred to in English-language publications as the Longmenshan Mountains, are a mountain range in Sichuan province in southwestern China. Geography The range runs in a roughly northeast to southwes ...

Sichuan Sichuan (; zh, c=, labels=no, ; zh, p=Sìchuān; alternatively romanized as Szechuan or Szechwan; formerly also referred to as "West China" or "Western China" by Protestant missions) is a province in Southwest China occupying most of t ...

province in southwestern

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...

. The strike of the fault plane is approximately NE. Motion on this fault is responsible for the uplift of the mountains relative to the lowlands of the

Sichuan Basin The Sichuan Basin (), formerly transliterated as the Szechwan Basin, sometimes called the Red Basin, is a lowland region in southwestern China. It is surrounded by mountains on all sides and is drained by the upper Yangtze River and its tributar ...

to the east. Representing the eastern boundary of the Qinghai-Tibet Plateau, it is a border formation between the Bayan Kola block in the Plateau and the

South China block The Yangtze Plate, also called the South China Block or the South China Subplate, comprises the bulk of southern China. It is separated on the east from the Okinawa Plate by a rift that forms the Okinawa Trough which is a back-arc basin, on the so ...

in the

Eurasian Plate The Eurasian Plate is a tectonic plate that includes most of the continent of Eurasia (a landmass consisting of the traditional continents of Europe and Asia), with the notable exceptions of the Indian subcontinent, the Arabian subcontinent an ...

. The 2008 Wenchuan, 2013 Lushan and 2022 Ya'an earthquakes occurred along this fault. A study by the China Earthquake Administration (CEA) states:

"The late-Cenozoic deformations in this fault (''that caused the 2008 Wenchuan earthquake'') are concentrated in the Guanxian- Jiangyou fracture (hill-front fracture), Yingxiu- Beichuan fracture (mid-fracture),
Wenchuan Wenchuan County is a county in Ngawa Tibetan and Qiang Autonomous Prefecture, Sichuan, People's Republic of China. The county has an area of , and a population of 100,771 as of 2010. Wolong National Nature Reserve is a protected area located i ...
-
Mao County Mao County or Maoxian (; ; Qiang: ʂqini) is a county in Ngawa Prefecture, Sichuan Province, China. It has an area of 3,903 and a population of 106,700 as of 2006. 88.9% of the population are Qiang people. The county seat is Fengyi (). Natu ...
fracture (hill-back fracture), and their related folds. The recent M_s 8.0 earthquake occurred on the Yingxiu-Beichuan fracture, as a result of Longmenshan thrust pushing southeastward combined with clockwise shears. Since Holocene (10,000), Yingxiu-Beichuan fracture has had evident activities. Its long-term geological slip rate is slower than 1 mm per year. GPS observations confirm the current structural deformation of the Longmenshan formation to be characterized by thrust and right-handed shears, but with a low deformation rate. Therefore, Longmenshan formation and its internal fractures constitute a special type that has low earthquake frequences but the potential to cause super strong earthquakes."

Morphology

The American Geophysical Union publication ''Tectonics'' describes the 5 km high escarpment thus:

"In the Longmen Shan region, however, the topographic margin of the
Tibetan Plateau The Tibetan Plateau (, also known as the Qinghai–Tibet Plateau or the Qing–Zang Plateau () or as the Himalayan Plateau in India, is a vast elevated plateau located at the intersection of Central, South and East Asia covering most of the Ti ...
is one of the world's most remarkable continental escarpments. Elevations rise from circa 600 m in the southern
Sichuan Basin The Sichuan Basin (), formerly transliterated as the Szechwan Basin, sometimes called the Red Basin, is a lowland region in southwestern China. It is surrounded by mountains on all sides and is drained by the upper Yangtze River and its tributar ...
to peaks exceeding 6500 m over a horizontal distance of less than 50 km. Regional topographic gradients typically exceed 10% along this mountain front and rival any other margin of the plateau."

References

External links

Map of faults in SW China - MITSimplified geologic map of the Longmen Shan region
of the eastern margin of the Tibetan Plateau. *China Virtual Museum of Earthquakes, map charting th

{{East Asia plates Geology of China Seismic faults of Asia Geography of Sichuan Cenozoic China