|Earthquakes||~174-374 AD, 1092 AD, 1920, 1927, 2022|
|Type||sinistral strike-slip fault|
The Haiyuan Fault is a major active intracontinental strike-slip (sinistral) fault in Central Asia.
The Haiyuan Fault forms part of the northeastern boundary of the Tibetan Plateau, which is an area of continental crust that has been thickened by the ongoing continental collision between the Indian Plate and the Eurasian Plate. The Haiyuan Fault extends for approximately 1,000 km from the central Qilian Shan in the west, to the Liupan Shan, in the east. It is one of the group of structures that accommodates the overall eastward spreading of the plateau, that also includes the Altyn Tagh Fault, Kunlun Fault and the Xianshuihe fault system.
It is characterized by left-lateral strike-slip motion along its length, the motion transits to thrust at the eastern end, accommodated by the Liupanshan Fault. The average slip rate along the Haiyuan Fault is 3.2–9 mm/yr.
The Tianzhu seismic gap is a 260 km long, unruptured segment on the western end of the fault. It has not seen any major earthquakes for the past 1,000 years and was identified as a seismic gap. It poses a high risk for the capacity of large earthquakes. An earthquake recurrence period of roughly 1,000 years has been suggested, with the last earthquakes on that section dated at 1092 AD and 174 or 374 AD. Locking depth of the fault range from 7.1–21.8 km.
At the western end of the 1920 earthquake surface rupture, and between the Tianzhu seismic gap (from 37.11° N, 103.68° E to 37.00° N, 104.15° E) lies a 30–40 km section of the fault that displays a phenomenon known as an aseismic creep at shallow depths.
Main article: 1920 Haiyuan earthquake
On the evening of December 16 1920, the a M7.8–8.5 earthquake struck Haiyuan County, killing over 270,000 people. Shaking intensity reached a maximum of XII (Extreme), the uppermost limit on the Modified Mercalli intensity scale. The fault ruptured for a length of nearly 240 km in this event.
Main article: 1927 Gulang earthquake
A magnitude 7.7 quake struck Gansu Province on the morning of May 22, 1927, the earthquake occurred on a different segment from the one involved in the 1920 quake. This earthquake caused the deaths of more than 40,000 people, and 200,000 livestock.
Main article: 2022 Qinghai earthquake
An Mw 6.6 or Ms 6.9 earthquake struck Menyuan County in January 2022, causing little damage and few minor injuries. The earthquake was felt with a maximum intensity of IX on the China seismic intensity scale (IX on the Modified Mercalli intensity scale) over a 157 km3 area.
It generated a 22 km-long surface rupture along the Lenglongling segment of the Haiyuan Fault. On-site investigations found up to 2.1 meters of left-lateral strike-slip offsets. The surface rupture also crossed the tunnel of a high-speed railway linking Lanzhou to Ürümqi, causing severe damage to a bridge and the tracks. Modelling of the earthquake suggest it had a maximum coseisic slip of around 3.5 meters at a depth of 0–10 km along the rupture.
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