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

Abstract

According to volume 18 (<i>Xuanzong Ji Tang</i>) of the historical book entitled the <i>Old Book of Tang</i>, the Hetao area of Inner Mongolia experienced a large earthquake in AD 849. However, previous work on that earthquake contains many discrepancies regarding its epicenter location, magnitude, deaths, and intensity. While exploring active faults in Baotou City, the present authors mapped the Daqing Mountain piedmont fault geologically. Based on previous work, several seismic deformation traces of more than 1000 years ago were found, and dating tests were conducted. The research showed the Daqing Mountain piedmont fault zone to be the seismogenic structure of the AD 849 earthquake. The length of earthquake surface rupture zone was around 80 km, and the macro epicenter was located in the active fault. The deformation center was located at 40.6°N, 110.2°E. By collecting and analyzing more historical data about the AD 849 earthquake, reinterpreting some existing historical data, and re-examining the contradictory numbers of deaths in the historical data, the present analysis concludes that around 10,000 people were dead. It is suggested that this earthquake had a magnitude of 7½. According to the revised seismic parameters and the paleoearthquake recurrence period of the Daqing Mountain piedmont fault, the boundary of some potential seismic sources zone in the Baotou area are adjusted and the recurrence period of <i>M</i>8 and <i>M</i>7.5 are re-calculated.