The Zhongwei-Tongxin fault or Tianjingshan fault is an arcuate sinistral (left-lateral)

strike-slip In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

zone, forming one of the major structures on the northeastern margin of

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 ...

. Six paleoearthquake events in the past 14,000 years have been recorded along the Zhongwei-Tongxin fault zone. Among the earthquakes recorded are the 1622 North Guyuan earthquake, which had a magnitude of 7.0 and mid-seismogenic depth of about , the 1709 Zhongwei earthquake, which had a magnitude of 7.5.

Tectonic setting

The Zhongwei-Tongxin fault is one of the structures that accommodates the eastward spreading of the thickened crust of the Tibetan Plateau, the result of the ongoing

collision In physics, a collision is any event in which two or more bodies exert forces on each other in a relatively short time. Although the most common use of the word ''collision'' refers to incidents in which two or more objects collide with great fo ...

between the

Indian Plate The Indian Plate (or India Plate) is a minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian Plate broke away from the other fragments of Gondwana , began mov ...

and 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 and ...

. The northeastern margin of the Tibetan Plateau is marked by a combination of sinistral (left-lateral) strike-slip faults and

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 ...

s. The largest of the strike-slip faults is the 1,000 km long WNW–ESE trending Haiyan fault, which links to the east with the northern end of the Liupanshan Fault zone, a

fold and thrust belt A fold and thrust belt (FTB) is a series of mountainous foothills adjacent to an orogenic belt, which forms due to contractional tectonics. Fold and thrust belts commonly form in the forelands adjacent to major orogens as deformation propagates ou ...

that accommodates the eastward motion of the plateau against the

Ordos Block The Ordos Block is a crustal block, that forms part of the larger North China Block (NCB). It is surrounded by active fault systems and has been a distinct block since at least the Mesozoic. It is bordered to the west by the Alxa Block, the west ...

. To the north of the western part of the Haiyuan Fault, the northern boundary of the

Qilian Shan The Qilian Mountains (, also romanized as Tsilien; Mongghul: Chileb), together with the Altyn-Tagh (Altun Shan) also known as Nan Shan (, literally "Southern Mountains"), as it is to the south of Hexi Corridor, is a northern outlier of the Kun ...

is formed by WNW–ESE trending thrust faults of the Hexi Corridor. Near Gulang, the Haiyuan Fault splays onto the west–east trending Gulang Fault, which continues to the east as the four segments of the Zhongwei-Tongxin fault.

Geometry

The fault zone extends for about 240 km from just north of Jingtai in the west to near

Tongxin Tongxin County (, Xiao'erjing: طْوثٍ ثِيًا) is a County (People's Republic of China), county under the administration of the prefecture-level city of Wuzhong, Ningxia, Wuzhong in the central part of the Ningxia Hui Autonomous Region of th ...

in the east. Four main segments have been recognised, the western, central, eastern and southeastern. The western and central segments have mainly sinistral

motion, accommodating movement between the Tiangjingshan Block (TJSB) and the Alashan Block to the north. The eastern and southeastern segments are mainly

s in type, accommodating shortening between the TJSB and the

to the east.

Slip rates

Slip rates along the Zhongwei-Tongxin fault have been estimated from the offset of landforms, the analysis of past earthquakes by trenching and

GPS The Global Positioning System (GPS), originally Navstar GPS, is a Radionavigation-satellite service, satellite-based radionavigation system owned by the United States government and operated by the United States Space Force. It is one of t ...

data. The landforms, such as stream valleys, alluvial fans and river terraces, have been dated using

optically stimulated luminescence In physics, optically stimulated luminescence (OSL) is a method for measuring doses from ionizing radiation. It is used in at least two applications: * Luminescence dating of ancient materials: mainly geological sediments and sometimes fired pott ...

(OSL), as

radiocarbon dating Radiocarbon dating (also referred to as carbon dating or carbon-14 dating) is a method for determining the age of an object containing organic material by using the properties of radiocarbon, a radioactive isotope of carbon. The method was dev ...

cannot be used because of the extremely dry conditions. These three approaches give consistent results of 1.1±0.2 mm per year of sinistral strike-slip for the fault zone over a range of timescales from decades for the GPS data, up to a million years from offset markers.

Seismicity

Paleoseismic investigations of the Zhongwei-Tongxin fault zone have revealed evidence of three major earthquakes. The most recent of these has been identified as the 1709 Zhongwei earthquake, with the earlier events being dated to 5,450±238 years

Before Present Before Present (BP) years, or "years before present", is a time scale used mainly in archaeology, geology and other scientific disciplines to specify when events occurred relative to the origin of practical radiocarbon dating in the 1950s. Becaus ...

(BP) and 8,850±350 years BP.

References

{{reflist Geology of China Seismic faults of Asia