Earthq Sci (2019)32: 170–178 170 doi: 10.29382/eqs-2019-0170-07 Parameters of the AD 849 earthquake east of Baotou City in Inner Mongolia and the adjustion of the potential seismic sources zone spatial distribution functions* Ji Wang1,* Zhanwu Gao1 Wei Xu1 Zhaode Yuan2 Zhicheng Liu1 Xiaoliang Zhang1 1 China Earthquake Disaster Prevention Center, Beijing 100029, China 2 Institute of Geology, China Earthquake Administration, Beijing 100029, China Abstract According to volume 18 (Xuanzong Ji records the following: “Xinsi Age in October of the third Tang) of the historical book entitled the Old Book of Tang, the year of Dazhong Emporer in Tang Dynasty (October 20, Hetao area of Inner Mongolia experienced a large earthquake AD 849), the Jingshi (Xi'an City) felt earthquake shock in AD 849. However, previous work on that earthquake contains many discrepancies regarding its epicenter location, and Hexi, Tiande, Ling, Xia felt especially serious. magnitude, deaths, and intensity. While exploring active Thousands of people were killed”. This indicates the faults in Baotou City, the present authors mapped the Daqing historical occurrence of a great earthquake in the north of Mountain piedmont fault geologically. Based on previous China, but the scant historical records and the nearly 1200 work, several seismic deformation traces of more than 1000 years that have elapsed since the earthquake mean that years ago were found, and dating tests were conducted. The little trace of it remains. Nie and Li (1991), and Nie et al. research showed the Daqing Mountain piedmont fault zone to (1996, 2008, 2010) studied the AD 849 earthquake in be the seismogenic structure of the AD 849 earthquake. The length of earthquake surface rupture zone was around 80 km, detail and suggested the Daqing Mountain piedmont fault and the macro epicenter was located in the active fault. The as the causative fault. His work showed that the earthquake deformation center was located at 40.6°N, 110.2°E. By fault starts at Haolaigou in the west and extends eastward collecting and analyzing more historical data about the AD intermittently to the Baiyunchahan area of the Tumed Left 849 earthquake, reinterpreting some existing historical data, Banner. The length of the surface rupture zone is about and re-examining the contradictory numbers of deaths in the 100 km. The accumulated vertical displacement measured historical data, the present analysis concludes that around 10,000 people were dead. It is suggested that this earthquake by Nie et al. (2010) was more than 2.3 m, from which he had a magnitude of 7½. According to the revised seismic judged that the epicenter intensity could have been as high parameters and the paleoearthquake recurrence period of the as intensity of Ⅹ degree. Daqing Mountain piedmont fault, the boundary of some However, Nie et al. (2010) estimated the death toll potential seismic sources zone in the Baotou area are adjusted being only in the dozens, which seems somewhat and the recurrence period of M8 and M7.5 are re-calculated. inconsistent with the scale of economic and population damage caused by a major earthquake at that time. In the Keywords: earthquake; rupture traces; parameters; AD 849; present study, data about this earthquake were collected Daqing Mountain; piedmont fault systematically and then sorted and examined. Here in, we discuss the epicenter location, the seismogenic structure and isoseisms, the number of death toll, and the magnitude 1 Introduction of the earthquake. Having revised the seismic parameters, we adjust the boundary and parameters of some seismic potential sources zone in the Baotou area. Volume 18 (Xuanzong Ji) of the Old Book of Tang * Received 22 May 2019; accepted in revised form 6 January 2020; 2 Epicenter of AD 849 Baotou east published 29 May 2020. earthquake * Corresponding author. e-mail: [email protected] © The Seismological Society of China and Institute of Geophysics, China Earthquake Administration 2019 To determine the epicenter of the AD 849 east Baotou Earthq Sci (2019)32: 170–178 171 earthquake, we begin by establishing the present locations located on the East Bank of the Yellow River in the of some of the places named in historical books. Speci- northwest of Wuzhong City, Ningxia Hui Autonomous fically, Jingshi or Shangdu refers to the capital City of the Region (Lu et al., 1993). Tang Dynasty, which is now Xi’an City in Shaanxi Prov- Yanzhou City is located in Dingbian County in ince. Meanwhile, Zhenwu and Tiande were important mili- Shaanxi Province. tary organizations on the northern frontier of the middle to Xiazhou is now Baichengzi Village of Hongdunjie late Tang Dynasty (AD 755–907) and were also known as Town in Jingbian County in Shaanxi Province. the Zhenwu Army and Tiande Army, respectively. Yunjia Town, namely, Yunjiaguan pass, this showed The Zhenwu Army, established in the second year of that Yunjiaguan pass belonged to Jinhe County. It should the Jinglong Age of the Tang Dynasty (AD 708), located be in the area of Helinger County of Inner Mongolia in Tuchengzi township, Helinger county, Inner Mongolia, (Table 1). according to the Eighteenth Geographical records of the In summary, the locations of heavy death toll due to Old Book of Tang (Liu, 1975 a, b). the earthquake were all in and around the Hetao Basin. Tiande Army, belonging to Guan-nei Dao, Tang Considering the seismic geological conditions of the Hetao Dynasty, was stationed on the south bank of Wuliangsu Basin and its surrounding areas, we conclude that the Sea, the Urad Front Banner, Inner Mongolia. earthquake almost certainly occurred in the Hetao Basin, a Lingwu, namely, Lingzhou City of Tang Dynasty was conclusion that is supported by previous research (Nie and Table 1 Ancient places name and its modern location and destruetion associated with AD 849 earthquake No. Ancient place name Modern location Destruction Intensity 1 East Shouxiang City Old Town of Tuoketuo County, Thousands of soldiers X Inner Mongolia were dead 2 Chanyu Grand Frontier Command Tuchengzi Township, Helinger County, (location of Zhenwu Army) Inner Mongolia 3 Shengzhou City South bank of Yellow River in Zhungeer Banner, Inner Mongolia Army towns and farm 4 Mid Shouxiang City North bank of Yellow River in south of Baotou City, houses destroyed ≥VIII Inner Mongolia 5 Tiande Army South coast of Wuliangsu Sea in Wulat Qian Banner, Inner Mongolia 6 Yunjia Town Helinger County, Inner Mongolia Two captains and tens soldiers were killed 7 West Shouxiang City Wulat Qian Banner of Inner Mongolia Earthquake had VII sound, farm houses 8 Linzhou Shenmu County, Shaanxi Province destroyed 9 Ma Yi Shuozhou City, Shanxi Province 10 Lingzhou East bank of Yellow River in northwest of Wuzhong Earthquake was strong VI City, Ningxia Hui Autonomous Region and may have caused some damages 11 Xiazhou Baichengzi Village, Hongdunjie Town, Jingbian County, Shaanxi Province 12 Yanzhou Dingbian County, Shaanxi Province 13 Jingshi Xi′an City, Shaanxi Province Felt a little shock 14 Tongzhou Dali County, Shaanxi Province Felt a little shock 15 Yulin Yulin City, Shaanxi Province Felt a little shock 16 Huaiyuan Hengshan County, Shaanxi Province Felt a little shock <VI 17 Xining Xining City, Qinghai Province Felt a little shock 18 Zhili Hebei Province Felt a little shock 19 Shanxi Shanxi Province Felt a little shock 172 Earthq Sci (2019)32: 170–178 Li, 1988, 1991; Nie et al., 1996, 2008, 2010). platform has a 14C age of 2507±122 a, and the vertical displacement of the fault is 0.85 m (Nie et al., 2010). 3 Fracture range and location of 4) North of the expressway bridge of Yongfu Village, a epicenter region Holocene alluvial fan (with a 14C age of 4610±90 a at the top) is arched and deformed, and a group of more than 10 faults with different scales has developed (Nie et al., Next, we discuss the seismogenic structure and more- 2010). accurate epicenter location of this earthquake based on the 5) On the front of the Hazigai diluvial fan in Goumen results of recent seismogeological studies. Nie et al. (1996) Town of Tumed Right Banner, the fault dislocation strata uncovered 6 ancient earthquake events since the Holocene have a 14C age of 2310±100 a (Jiang et al., 2001). by digging a trench in an aluminum plant. In the middle 6) In the Shangdalai trench in the Tumed Left Banner, and western segments of the fault, traces of seismic the fault dislocation was around 1 m from the surface. The deformation about 1000 years ago have been found in layer contains Han Dynasty pottery tablets, and its 14C age many places. The main relics are as follows. is 2115±105 a (Wu et al., 1995). 1) A fault scarp of 2.6–2.7 m in height is developed in 7) At the front of the Baiyunchahan estuary alluvial fan the rear edge of the level-I platform in the west of Xuehai in Qianzhan Village of Tumed Left Banner, the age of 14C Gully, whose strike approaches nearly E-W and extends to fault dislocation was 1160±100 a (Jiang et al., 2001). 500 m. The latest activity of faults controlling steep ridges The aforementioned seismic deformation traces along 14 disrupted the grayish-brown sandy soil layer with a C the Daqing Mountain piedmont fault are distributed age of 1640±112 a, with a fault displacement of 1.2 m (Nie between the Donghe District of Baotou City and the et al., 2010). Tumed Left Banner of Hohhot City, with a length of 2) In the north trench trough of the Baotou Aluminum around 80 km from east to west and concentrated in the Plant (Nie et al., 1996), the latest fault activity is a stratum area from the Baotou Aluminum Plant to Yongfu Village.