Abstract:

The Lajia Ruins, often called the “Pompeii in the East”,situated in Minhe County, Qinghai Province, is well known as an archaeological site documenting a catastrophic event approximately 3,900 years ago. The causation of the disasters responsible for the destruction of the Lajia settlement has been in hot debate for an extended period. Various points of view regarding “flooding causes” has been gained acceptance within the general public. However, is the catastrophic event indeed linked to flooding? The 6.2-magnitude earthquake struck in Jishishan County, Gansu Province on December 18, 2023, with its epicenter located a mere 16 kilometers from the Lajia Ruins. This seismic event not only substantially damaged the Lajia Ruins Museum but also triggered mudflows in Jintian Village and Caotan Village, Zhongchuan Town, Minhe County, just 5 kilometers away from the Lajia Ruins. This catastrophic event led to the direct burial of residential structures and villagers, potentially representing a replication of the formative processes that gave rise to the Lajia Ruins. Consequently, it emerges as a pivotal empirical material for comparative studies investigating the causative factors underlying the genesis of the Lajia Ruins. Through conducting field investigations and comprehensive studies of the seismic disaster, it is conceivable that contemporary insights may shed light on the longstanding enigma surrounding the genesis of the Lajia Ruins. The earthquake has induced an upward surge of groundwater from the ancient riverbed gravel layers beneath the loess, causing the liquefaction of the loess and the rapid downstream flow of mud through gullies. As the mudflow encountered obstacles when passing through Caotan Village and Jintian Village, it overflowed the gullies, destroying some houses and even burying villagers. The distinctive geological stratigraphy and the abundance of groundwater, triggered by seismic activities, resulted in soil’s liquefaction and mudflows’ formation, constituting crucial factors in the genesis of seismic disasters in Zhongchuan Town. Field investigations indicated the tragic burial of a family of five in Caotan Village was not the result of a typical “sand surge”, nor does it exhibit traces of “flooding”. Instead, it is attributed to secondary seismic hazards, specifically mudflows induced by the earthquake. Combined with the preservation status of cultural remains and sedimentary characteristics at the Lajia Ruins, inference suggests that the ancient earthquake 3,900 years ago, along with the resultant liquefaction of soil and the rapid flow of mud, provides a plausible explanation and reconstruction for the instantaneous catastrophe at the Lajia Ruins. The formation of the Lajia Ruins is likely unrelated to the mountainous flash floods induced by heavy rainfall and certainly not caused by the purported megaflood.

Key words: Lajia Ruins, Jishishan Earthquake, liquefied mudflow, instantaneous catastrophe, northern margin of Lajishan Mountain Fault, Yellow River