Major left-lateral strike-slip structures occur in the Tibetan Plateau as a result of the India–Asia collision.[4] These faults, including the Altyn Tagh, Haiyuan, Kunlun, Karakoram and Xianshuihe faults, accommodate crustal deformation within the Tibetan Plateau. One of these fault systems, the Haiyuan Fault, runs 1,000 km (620 mi) along the plateau's northeastern edge.[5]
Earthquake
The earthquake hit at 19:05:53 Gansu-Sichuan time (12:05:53 UTC),[6] reportedly 8.25 Mw[7] or 7.8 ML, and was followed by a series of aftershocks for three years. The often cited magnitude in scientific literature is M 8.5 which has been regarded as an overestimate due to the limited technological advancements and instrumentation during the period which the earthquake occurred. On the moment magnitude scale which measures an earthquake with respect to its physical parameters, it is estimated at Mw 7.9.[8] The International Seismological Centre also catalogs the earthquake at Mw 7.9.[9]
About 230 km (140 mi) of surface faulting was seen from Lijunbu through Ganyanchi to Jingtai. There were over 50,000 landslides in the epicentral area and ground cracking was widespread. Some rivers were dammed; others changed course.[10]Seiches from this earthquake were observed in two lakes and three fjords in western Norway.[3]
Field observations in the 1980s found 237 km (147 mi) of surface rupture along the Haiyuan Fault with a maximum horizontal offset of 6.5 m (21 ft) in the middle section of the rupture zone. The earthquake ruptured the section of the Haiyuan Fault between the Laohushan segment in the west and Liupanshan Thrust Fault to the east. The earthquake's epicenter is also likely near Haiyuan which is supported by the seismic intensity distribution.[4]
Since 2003,[11] Chinese seismologists have calculated 258,707~273,407 to be the empirical verifiable range of death toll.[2] Older sources put the deaths to be 234,117[12] or 235,502.[13] Either way, it is one of the most fatal earthquakes in China, in turn making it one of the worst disasters in China by death toll.
Many more perished because of cold: frequent aftershocks caused the survivors to fear building anything other than temporary shelters, and a severe winter killed many who had lived through the original earthquake.[14]
^Han, Longfei; Liu-Zeng, Jing; Yao, Wenqian; Shao, Yanxiu; Yuan, Zhaode; Wang, Yan (November 2021). "Coseismic slip gradient at the western terminus of the 1920 Haiyuan Mw 7.9 earthquake". Journal of Structural Geology. 152: 104442. doi:10.1016/j.jsg.2021.104442.
^National Geophysical Data Center / World Data Service (NGDC/WDS): NCEI/WDS Global Significant Earthquake Database. NOAA National Centers for Environmental Information. "Significant earthquake Information". doi:10.7289/V5TD9V7K. Retrieved 2024-03-21.
^"海原断裂带强震发生概率的评估方"(PDF). 地震学报: 1048,1050. 2014. Archived(PDF) from the original on 2021-05-24. Retrieved 2021-05-24. 本文直接采用1920年海原地震的矩震级W8.25
Xu, Xiurong; Zhang, Zhenguo; Hu, Feng; Chen, Xiaofei (2019), "Dynamic Rupture Simulations of the 1920 Ms 8.5 Haiyuan Earthquake in China", Bulletin of the Seismological Society of America, 109 (5): 2009–2020, Bibcode:2019BuSSA.109.2009X, doi:10.1785/0120190061, S2CID203134903