The Xianshuihe fault system or the Yushu-Ganzi-Xianshuihe fault system is a major active sinistral (left-lateral) strike-slip fault zone in southwestern China, at the eastern edge of the Tibetan Plateau. It has been responsible for many major earthquakes, and is one of the most seismically active fault zones in China.
The Xianshuihe fault system lies within the complex zone of continental collision between the Indian Plate and the Eurasian Plate. It forms one of a set of sinistral fault zones that help accommodate the eastward spreading of the Tibetan Plateau. [1] The fault zone defines the northern and eastern edges of the Qiangtang block (also known in part as the Sichuan-Yunnan block), and the southeastern boundary of the Bayan Har block. To the southeast it also forms the western margin of the South China Block. [2]
The Xianshuihe fault system comprises several distinct segments, with an overall length of 1,400 km. The main segments are the Dangjiang, Yushu, Ganzi, (or Ganzi-Yushu), the Xianshuihe, the Anninghe-Zemuhe, and the Xiaojiang faults. [3] [4] Each of these faults are themselves divided into smaller segments. The fault system has also been divided into a western part and an eastern part, with the division between the Ganzi and Xianshuihe segments. [5]
This segment is about 170 km in length. At its western end it connects to the Fenghuoshan Fault, which continues on into a poorly studied region. At its eastern end it overlaps with the Yushu segment to which it links through a right-stepping compressional stepover of 25 km, which is associated with a 20 km wide zone of uplift. The easterly 100 km of the segment are thought to have ruptured during the M7.6 1738 Dangjiang earthquake. [4]
The total length of this segment is about 170 km. At its eastern end the Yushu segment connects through to the Ganzi segment through the Batang Basin. The segment has two main sections that are linked via a left-stepping extensional stepover through the Longbao Lake Basin, a pull-apart structure 30 km x 6 km in size. In 2010 about 50–80 km of this segment ruptured during the M7.1 2010 Yushu earthquake. [6]
This approximately 300 km long segment is subdivided into three sections. The 70 km long Denke section that ruptured during an M7.0–7.5 earthquake in 1896, the 170 km long Manigange section that ruptured in a M7.7–8.0 earthquake in 1854 and the 65 km long Ganzi section, which ruptured in a M7.1–7.3 earthquake in 1866. The eastern end of the segment overlaps with the Xianshuihe segment via a 45 km left-stepping extensional stepover. [7] [8]
This approximately 350 km long northwest-southeast trending segment is divided into five main sub-sections, from northwest to southeast, the Luhuo, Daofu, Qianning, Kangding and Moxi. There is evidence of aseismic creep along much of this segment. [9] An overall slip rate of 12 mm per year has been estimated for this segment from the analysis of InSAR data. In detail there is evidence of an increase from the northwestern end of the segment, consistent with ongoing shortening within the Bayan Har block. [5]
A series of historical earthquakes have been associated with the Xianshuihe segment, the most recent events on each section were 1786 (M7.7 Moxi), 1893 (M7.0 Qianning), 1923 (M7.3 Daofu), 1973 (M7.6 Luhuo) and 2014 (M6.3 Kangding). [5]
This ~250 km long segment is formed of two main sections; the Anninghe, which runs north–south in the north and the Zemuhe that runs NNW–SSE, linking together at a sharp bend. [10] There is an additional fault that lies further east, the Dalingshan Fault. [11] The Anninghe section has an estimated slip rate of 3.6–4.0 mm per year while that for the Zemuhe section is 3–5 mm per year. Paleoseimological investigations suggest that some of the large earthquake, such as those in 814 and 1850 ruptured across the bend between the two sections, while some, such as that in 1536 only ruptured the Anninge section. [10]
The southernmost segment of the fault system runs for about 400 km from the end of the Zemuhe section to its junction with the right-lateral Red River Fault. The Xiaojiang Fault is subdivided into northern, central and southern sections. The northern section consists of a single fault strand, the central section of two main parallel fault strands and the southern sections of multiple fault strands. The Quaternary slip rate for the central and northern segments is estimated as 10–16 mm per year and currently 7–10 mm per year. Historical earthquake along this segment include a M8.0 event in 1833 and a M7.8 event in 1733. [11]
Movements on this fault system have been responsible for many large historical earthquakes, with more than 20 events of magnitude greater than 6.5 since 1700. [12] Some of these earthquakes have formed linked sequences, with each event being triggered by the previous one due to stress changes. [13]
Like the San Andreas Fault in California, the eastern part of the Xianshuihe fault system exhibits a behavior called aseismic creep. The Xianshuihe fault creeps at a rate of a few mm/yr between earthquakes. [14]
In seismology, a supershear earthquake is an earthquake in which the propagation of the rupture along the fault surface occurs at speeds in excess of the seismic shear wave (S-wave) velocity. This causes an effect analogous to a sonic boom.
An earthquake occurred in China on 14 November 2001 at 09:26 UTC, with an epicenter near Kokoxili, close to the border between Qinghai and Xinjiang in a remote mountainous region. With a magnitude of 7.8 Mw, it was the most powerful earthquake in China for 5 decades. No casualties were reported, presumably due to the very low population density and the lack of high-rise buildings. This earthquake was associated with the longest surface rupture ever recorded on land, ~450 km.
The 2010 Yushu earthquake struck on April 14 and registered a magnitude of 6.9 Mw or 7.1 Ms. It originated in Yushu, Qinghai, China, at 7:49 am local time. According to the Xinhua News Agency, 2,698 people were confirmed dead, 270 missing and 12,135 injured, 1,434 of them severely. The epicenter was located in Rima village (日玛村/日麻村), Upper Laxiu township (上拉秀乡) of Yushu County, in remote and rugged terrain, near the border of Tibet Autonomous Region, about 30 km from Gyêgu town or Jyekundo, the seat of Yushu County, and about 240 km from Qamdo. The epicenter was in a sparsely populated area on the Tibetan plateau that is regularly hit by earthquakes.
The 1927 Gulang earthquake occurred at 06:32 a.m. on 23 May. This 7.6 magnitude event had an epicenter near Gulang, Gansu in the Republic of China. There were 40,912 deaths. It was felt up to 700 km (435 mi) away.
The 1879 Gansu earthquake occurred at about 04:00 local time on 1 July. It had an estimated magnitude of 8.0 on the Ms scale and a maximum perceived intensity of XI (Extreme) on the Mercalli intensity scale. The epicenter was in Wudu District in southern Gansu, close to the border with Sichuan. It caused widespread damage and killed an estimated 22,000 people.
An earthquake occurred on 1 June 1786 in and around Kangding, in what is now China's Sichuan province. It had an estimated magnitude of about 7.75 and a maximum perceived intensity of X (Extreme) on the Mercalli intensity scale. The initial quake killed 435 people. After an aftershock ten days later, a further 100,000 died when a landslide dam collapsed across the Dadu river.
The Haiyuan Fault is a major active intracontinental strike-slip (sinistral) fault in Central Asia.
The 1973 Luhuo earthquake struck near the town of Zhaggo in Garzê Tibetan Autonomous Prefecture of Sichuan Province, China on February 6, 1973, with a magnitude of 7.6 Ms. The earthquake had a maximum intensity of X (Extreme) on the Modified Mercalli intensity scale. It resulted in between 2,175 and 2,204 deaths and a further 2,743 injuries. Serious and widespread destruction occurred in Luhuo County.
The 2021 Maduo earthquake, also known as the 5.22 earthquake struck Madoi County in Qinghai Province, China on 22 May at 02:04 local time. The earthquake had a moment magnitude and surface-wave magnitude of 7.4. Highway bridges, roads and walls collapsed as a result of the earthquake. According to an anonymous source, at least 20 people were killed, 300 were injured, and 13 were missing. Officials stated that there were no deaths but 19 people sustained minor injuries. It was the strongest in China since 2008. It was assigned a maximum intensity of X in Machali, Maduo County on the China seismic intensity scale and Modified Mercalli intensity scale. This earthquake was preceded by another unrelated earthquake that occurred 5 hours earlier in Yunnan.
The Bayan Har block or Bayan Kola block is an elongate wedge-shaped block that forms part of the eastern Tibetan Plateau. It is bounded to the southeast by the Longmenshan Fault, a major thrust fault zone, which forms the active tectonic boundary between the plateau and the Sichuan Basin. To the northeast, the boundary is formed by the Kunlun and Minjiang Faults juxtaposing the block against the Eastern Kunlun-Qaidam block and to the southwest by the Xianshuihe fault system forms its boundary with the Qiangtang block. All of these are major left-lateral strike-slip fault zones. The block is currently moving to the southeast relative to the South China block.
The 2020 Qiaojia earthquake occurred in Yunnan, China, 42 km west of Zhaotong on May 18, 21:48 local time. The moment magnitude 5.1 quake occurred at a depth of 10 km. Various buildings were damaged, and one house collapsed in Zhaoyang District. Four people were killed while 24 people were injured.
The 1850 Xichang earthquake rocked Sichuan Province of Qing China on September 12. The earthquake which caused major damage in Xichang county had an estimated moment magnitude of 7.3–7.9 Mw and a surface wave magnitude of 7.5–7.7 Ms . An estimated 20,650 people died.
The 1654 Tianshui earthquake occurred on July 21 in Tianshui, Gansu Province, Ming dynasty sometime between 21:00 and 23:00 local time. The event had an estimated moment magnitude of 7.0 and was assigned a maximum intensity of XI on the China seismic intensity scale. Resulting in extreme damage and affecting at least four provinces, the quake killed approximately 30,000 people.
The 1923 Renda earthquake occurred on March 24 at 20:40 local time between the counties of Daofu and Luhuo in Sichuan, China. The estimated Ms 7.3 earthquake was assigned a maximum modified Mercalli intensity scale rating of X (Extreme). Severe damage occurred in Sichuan, killing an estimated 4,800 people.
The 1955 Zheduotang earthquake, also known as the Kangding earthquake occurred on April 14 at 09:29:02 local time near the city of Kangding in the Garzê Tibetan Autonomous Prefecture, Sichuan. The earthquake had a moment magnitude of 7.0 and a surface wave magnitude of 7.1 and struck at a depth of 10 km. Severe damage occurred in Kangding with the loss of 70 lives.
A Mw 6.7 earthquake struck Luding County in Sichuan province, China on 5 September 2022 at 12:52:19 local time. The epicenter was located 226 km (140 mi) from Chengdu, or 43 km (27 mi) southeast of Kangding. Ninety-three people died, 424 were injured and 24 remained missing. More than 13,000 homes and other infrastructure were damaged or destroyed. It was the largest earthquake to strike the province since 2017.
The 1913 Eshan earthquake struck China's Yunnan Province on 21 December with a moment magnitude of 6.8 and maximum Mercalli intensity of IX (Violent). The shock devastated Eshan County; at least 942 people died and thousands of homes were destroyed. The earthquake ruptured along a section of the strike-slip Qujiang Fault.
On 23 December 1738 the province of Qinghai was struck by an earthquake with an estimated magnitude of 7.6 Mw. It ruptured the westernmost part of the Xianshuihe fault system, the Dangjiang segment. It led to 261–500 deaths.
The 1733 Dongchuan earthquake affected Yunnan in China on August 2. The earthquake, which had an estimated surface-wave magnitude of 7.75, damaged homes across the province.
On 20 March 1536, Xichang and Mianning, Sichuan, Ming dynasty, were struck by an earthquake with an estimated magnitude of 7.3 Ms. It had a maximum felt intensity of X (Extreme) on the Modified Mercalli intensity scale, and caused thousands of deaths.
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