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Journal of Asian Earth Sciences:Holocene paleoearthquakes on the Tianqiaogou-Huangyangchuan Fault in the northeastern boundary fault system of the Tibetan Plateau

2019/11/28 16:10:42

 About 55 to 45 Ma, India-Eurasian plate convergence collision constantly promote the Tibet Plateau uplifting and expanding towards the north and the east. The nearly 900-km-long Qilian-Haiyuan Fault System (QHFS) along the Qilian mountain is the most important boundary tectonic belt at the Tibet Plateau NE frontier, and also the tectonic boundary zone between the Tibetan, Ordos and Gobi Alashan blocks. The fault system can be divided into eastern and western sections. The western is a narrow fault (the Lenglongling fault, LLLF) along the Qilian Shan, and the eastern splays apart into two arc fault zones, of which the northern one mainly consists of the Tianqiaogou-Huangyangchuan Fault (THF, also known as the Gulang Fault) and the Xiangshan-Tianjingshan Fault (XTF)(Fig.1).

     Rupture behavior, one of the quantitative features of active fault, is fundamental for understanding crustal deformation mechanisms and assessing regional seismic risk. The 120-km-long Tianqiaogou-Huangyangchuan Fault (THF) is an important branch fault of the Qilian-Haiyuan Fault System (QHFS), the main boundary fault zone at the emerging northeastern margin of the Tibetan Plateau. Mismatching with the fast strike-slip rate, there is no M≥5 earthquake recorded along the THF.

   To obtain more precise information of the rupture behaviors along the boundary structure, Dr. SHI feng、HE honglin and the cooperators conducted a 1:50,000 active fault mapping and paleoearthquake trenching on the THF. The main conclusions are:

   

(1)Two trenches along the THF reveal at least 3 rupture events respectively. Based on the geometry of the fault trace and overlap analysis on the age ranges of all the events in the two trenches, at least 5 paleoearthquakes are suggested along the THF in the Holocene with age ranges of 485±675 BCE, 2085±295 BCE, 5590±1090 BCE, 7910±970 BCE, and 9975±955 BCE, respectively, and with moment magnitudes of 7.3-7.4.Confident ages of three rupture events on the fualt THF.

(2)The THF was not involved in the 1927 Gulang M8 earthquake.

(3)The THF is likely a seismic gap with a potential of M≥7 earthquakes.


Fig. 1. Seismotectonic map around the THF.

The results press in 《Journal of Asian Earth Sciences》(Feng Shi,Honglin He,Wei Gao et.al, 2019. Holocene paleoearthquakes on the Tianqiaogou-Huangyangchuan fault in the northeastern boundary fault system of the Tibetan Plateau. DOI: 10.1016/j.jseaes.2019.104049)

https://www.sciencedirect.com/science/article/pii/S1367912019304018