Using electrical resistivity tomography and surface nuclear magnetic resonance to investigate cultural relic preservation in Leitai, China

Leitai is a cultural relic site consisting of a loess platform built during the Qianliang dynasty (1700 years ago), Han dynasty tombs (1800 years ago) built on the lower part of the loess platform, and the Leitai Taoist temple built on the upper part of the loess platform during the Ming dynasties (500 years ago). Thus, this site has considerable historical and cultural research value. Over hundreds of years, some cultural relics at this site have been destroyed. For instance, blue bricks from the Han dynasty have been crushed and compressed due to the subsidence of the sealing soil on top of the tombs and have moistened and weathered due to the high humidity in the tombs. Additionally, soil cracking has occurred on the east side of the loess platform. Existing geological data indicate that the observed damage may be related to increases in the water content of the silty loess soil in the inner part of the platform due to rainfall infiltration. Electrical resistivity tomography (ERT) and surface nuclear magnetic resonance (SNMR), which are nondestructive detection methods, were applied to further investigate the causes of the observed damage and identify areas where damage is occurring. These methods successfully reveal an area of silty soil with high moisture content due to rainfall infiltration. The moisture content at this soil site is close to or exceeds the plastic limit determined by soil sample testing; as a direct or indirect result, local cultural relics have been destroyed. From 3D visualizations of 2D ERT inversion resistivity data and slice diagrams, we further delineated the regional boundaries of areas that pose a threat to the security of the cultural relics at Leitai. These results may serve as an important reference for the development of cultural relic conservation programs.