Archaeological Geophysics in China – A Historical Perspective

Abstract

Geophysical methods can efficiently identify and map archaeological features or changes in the matrix of a site. They have been extensively used in Chinese archaeological prospection since the survey for the Mausoleum of the Emperor Wanli of Ming Dynasty in mid-1950s. The evolution of archaeo-geophysics in China is closely linked to advances in emerging geophysical technology, the needs of non-destructive detection from the archaeological community and Chinese fast-growing economy. Throughout the past 70 years, researchers and practitioners witnessed the rapid development of geophysics in the field of Chinese Archaeology. In this chapter, we introduce some key archaeo-geophysical events, for example, a multi-geophysical project was performed by China Geological Survey (CGS), to evaluate the applicability and the effectiveness for archaeological characterisation at the Mausoleum of Qinshihuang, i.e. the first Emperor of the Qin Dynasty, during 2002 and 2003, the scale of which has been the largest in Chinese archaeo-geophysics so far. Besides, we divide these events into four periods, i.e. embryonic stage (1950s–1980), initial stage (1980–2000), development stage (2000–2010), and internationalisation stage (2010–present). Moreover, we also provide some significant case studies, namely ancient city sites and ancillary building remains, ancient tombs, cultural heritage protection, urban underground remains, and underwater archaeology. In a word, the development has paved the way to regular use of geophysical methods in almost all types of potential archaeological interests in China.

1 Introduction

Archaeology is the study of human activity through the recovery and analysis of material culture, using prospection, excavation and eventually analysis of data collected to learn more about the past. Most archaeological sites are not so conspicuous as the Pyramids and the Great Wall, rather they are buried underground or submerged under water all over the world. Archaeologists have to look for clues from the remains of mounds, stone buildings, city walls and other remnants left on the surface, such as pottery pieces, variegated soils, or suspicious caves. Furthermore, field excavations are required to investigate the ancient remains, and also to analyse the various relationships between the remains and the surrounding environment. While archaeological excavations are reproducible and protective, they are also invasive.

Modern Chinese archaeology began with the excavation and discovery of painted pottery remains in Yangshao Village, Mianchi County, Henan Province in 1921. Over the past 100 years, Chinese archaeologists have made a series of major discoveries, demonstrating the origin, development context, and splendid achievements of Chinese civilisation (An, 1992). Without any doubt, the development of Chinese civilisation occupies a unique place in the world. New archaeological discoveries in recent decades have attracted great attentions from the academic community and the public. However, because of the language barrier between China and Western countries, there are few English written review papers and monographs published for Western readers on Chinese archaeology, particularly on Chinese archaeo-geophysics. Therefore, we provide a brief introduction of key archaeo-geophysical events in China and some significant case studies, to commemorate and celebrate the many achievements during the 100th anniversary of the modern Chinese archaeology.

The traditional underground detection tool is the Luoyang Spade for Chinese field archaeologists, with a semi-cylindrical spade head and a long spade handle, which was originally invented and widely used by tomb robbers (e.g. Feng, 2016). However, it has become one of the most useful field archaeological tools in the past century in China, as different characteristics of soil and its inclusions can be identified by virtues of drilling cores with a few centimetres in diameter, and several meters, even more than 10 m in depth. With relative dense drilling, the distributions of potential archaeological features and deposits can usually be established, even without any excavations in a large-scale area. Of course, such detection can damage valuable cultural remains or disturb related archaeological strata inevitably and irreversibly. In such case, geophysical methods are useful because they can accurately identify, image and map the spatial extension and geometries of near surface archaeological features or changes in the matrix of a site in an absolutely non-destructive and cost-effective way (e.g. Bevan & Kenyon, 1975; Wynn, 1986; Jiang & Zhang, 2000; Gaffney, 2008; Zhao et al., 2015a). They are also recommended as valid methods to optimise location and planning of excavations (e.g. Forte & Pipan, 2008; Drahor et al., 2011; Zhao et al., 2013a).

1.1 Embryonic Stage: 1950s–1980

The development of large-scale infrastructure construction since the 1950s, opens a doorway for field archaeology. Archaeological and cultural relic research institutes were established consecutively by numerous provinces and autonomous regions. Besides, universities established the subject Archaeology to educate students in formal and systematic archaeological theories and methods. New concepts and technologies were also introduced to China in this period. The first application of geophysical methods in archaeology was the survey at the Mausoleum of the Emperor Wanli of the Ming dynasty in the mid-1950s (Jiang & Zhang, 1997). However, this survey did not provide satisfactory results. In 1978, the geophysical team from the Geology and Mineral Resources of Henan Province invited by the Museum of Henan Province, performed electrical resistance and magnetometer surveys at the Hougudui tomb in Gushi County. The subsequent excavations confirmed the geophysical results with the actual location of the main tomb chamber (Wu et al., 1988).

1.2 Initial Stage: 1980–2000

With the active recommendation from geophysical community to National Cultural Relics Administration, a wide variety of geophysical methods have increased been applied in archaeology since 1980. Projects included the identification of possible buried remains in large areas (e.g. Yan et al., 1998), mapping residual building foundations (e.g. Zhang, 1999a), locating and imaging ancient burial tombs (e.g. Zhang, 1996, 1999b), and characterising the degradation of architectural remains (e.g. Zhong, 1991). It is worth noting that integrated geophysical method, including side-scan sonar, magnetometry, and sub-bottom profiler, was used to detect ancient shipwrecks underwater in the sea of Liaoning Province in 1991. Of course, the scale of geophysical surveys was relatively small, and most of them were experimental in nature during this period, even though the geophysical results were a benefit for archaeological investigations and excavations (Jiang & Zhang, 1997).

1.3 Development Stage: 2000–2010

In order to facilitate an engagement of archaeologists/geophysicists in archaeo-geophysical prospection, Professors Hongyao Jiang and Limin Zhang, from Chinese Academy of Sciences, wrote and published the first book on this field in Chinese in 2000, entitled “Archaeo-geophysics”, mainly including the theoretic fundaments, basic concepts of the related methods and techniques, and especially case studies and achievements in China. At the same time, a large national archaeo-geophysical project was performed by China Geological Survey (CGS), to evaluate the applicability and the effectiveness for prospection of the Mausoleum of Qinshihuang, i.e. the first Emperor of the Qin Dynasty, during 2002–2003. The methods used included gravimetry, magnetometry, electrical resistivity tomography (ERT), electromagnetic induction (EMI), seismic reflection, ground penetrating radar (GPR), and surface nuclear magnetic resonance. The available literature also indicates that other integrated geophysical explorations, involving electrical resistance, magnetometry, and time-domain electromagnetic methods, were tested as early as 1987 and 1992 at the Mausoleum of Qinshihuang (e.g. Xia et al., 2004). However, for a specific target area, the scale of detection and the types of methods used by CGS have been the largest in Chinese archaeo-geophysics so far, and related geophysical results can be found in the book “Geophysical exploration for the underground palace of Emperor Qinshihuang Mausoleum”, published by Geological Press in 2005. Progressively, more and more geophysical projects have been applied to field archaeology (e.g. Xia et al., 2004; Su et al., 2007; Shen et al., 2008; Wang et al., 2008, 2010; Xu et al., 2008; Yu et al., 2009).

1.4 Internationalisation Stage: 2010–Present

Implementation of large scientific research project and publication of related monograph may imply that archaeo-geophysics was moving towards the vision of researchers as an independent subject in China. There were few international exchanges and presentations of geophysical results on this field before 2010 (e.g. Yuan et al., 2006). However, the situation has been changing dramatically in the past decade, as more and more case studies in Chinese Archaeo-Geophysics have been published in international journals and conference papers. These include the characterisation of ancient burial mounds using integrated geophysical methods (Zhao et al., 2019; Li et al., 2021), identification of buried earthen archaeological remains with GPR (Zhao et al., 2012, 2015b, 2021; Shi et al., 2015; Jiang et al., 2017; Zong et al., 2018), ERT (Zheng et al., 2013) and multi-frequency EMI (Tang et al., 2018) for large-scale site surveys, surface nuclear magnetic resonance for cultural heritage site protection (Lu et al., 2020, 2021), GPR characterisation of wooden cultural relics (Zhao et al., 2013b), and underwater archaeological investigation with GPR (Qin et al., 2018).

2 Geography and Soil Characteristics of China

From the perspective of macro-topography, China is surrounded by a series of natural barriers: woodlands, deserts and mountains are distributed in the north, west and southwest respectively, while the east and southeast are the sea. The northern border of China is open, as there are large gaps between the mountains, which have formed channels between China and neighbouring areas in ancient Chinese history. Besides, the topographic features of China are high in the west and low in the east. It is really rare that a country has both temperate and tropical zones, humid and arid areas, plains and mountains, and various types of natural soils and large areas of man-made soil (e.g. Fig. 1). According to natural conditions and current provincial boundaries, China can be divided into seven ecological regions: (1) North China in the middle and lower reaches of the Yellow River; (2) North-east China of the temperate zone; (3) the arid north-west region, including most Inner Mongolia; (4) Central China located in the middle and lower reaches of the Yangtze River; (5) humid subtropical and tropical South China; (6) humid subtropical and tropical south-west China; (7) and the Qinghai-Tibet Plateau at the west (Gong et al., 2014). Moreover, China has a wide variety of landforms and complex geological structures, made by internal forces such as geological foundations and neotectonics movements and external forces such as complex and changeable actions from climate, hydrology, and biology. For the land area of China, mountains account for about 33%, plateaus account for about 26%, basins account for about 19%, plains account for about 12%, and hills account for about 10%. In addition, other different types of landforms are developed, including mountain glaciers, frozen soil, aeolian sand dunes, loess, red soil, karst land, volcanoes, and coastal zones.

Fig. 1

Soil types of China. (Adapted from https://www.osgeo.cn/)

The subsurface sediments and soil conceal the tangible cultural remains of past societies that are fundamental as a source of information for archaeologist. In geophysical prospection, the differences in the physical properties of such soil, sediments and other buried interfaces such as archaeological remains are also very important to be able to select the best suite of detection methods. For example, soil moisture is a critical factor to be considered for GPR survey, as electromagnetic wave propagation is sensitive to attenuation that can be related to soil water content. From the perspective of soil moisture, associated with natural conditions and soil characteristics, the spatial distribution of Chinese soil can be divided into three major regions: moist soil in the east, sub-moist soil in the middle, and dry soil in the north-west. The north-west is a large area that can be cold and dry under the control of the north-west airflow in winter. The climate in the east is humid as it is affected by the south-east and south-west monsoons in summer. The north-western region is located in the interior of Eurasia, coupled with the influence of the Qinghai-Tibet Plateau and high mountains, resulting in drought and water shortage.

It is worth pointing out that China is a large agricultural country with a long history. Therefore, the depth and intensity of buried archaeological remains are considerable if compared with other countries in the world. In addition, the process of modern urban development has created a great deal of disturbance of the original soil and other deposits. During such construction work natural humus layers are stripped, some soil strata are inverted, and multiple anthropogenic deposits of different periods can be mixed and result in “multi-structured soil”.

3 Significant Case Studies of Archaeo-geophysics in China

3.1 Ancient City Sites and Ancillary Building Remains

The scale of remains related to ancient cities is quite rich in China given its complex and long history. Therefore, there are many potential targets to be detected by geophysical methods such as ash pits, ditches, ancient kiln sites, ancient roads, and building remains with different materials, like masonry, brick, or rammed earth. Electrical resistance, magnetometer and GPR surveys are used for rapid surface scanning, always accompanied with a positioning measurement by Real Time Kinematic Global Positioning System (RTK-GPS) or terrestrial Laser Scanner. Other less conventional geophysical methods have been also used in China to detect specific potential archaeological interests.

The location and detailed characterisation of rammed earth sites in Chinese archaeology is an important topic due to the large temporal and spatial distributions of such type of sites. These include ancient city walls, large mausoleums, and building foundations. Yan et al. (1998) successfully surveyed the ancient city walls built during the Eastern Zhou Dynasty in Shangqiu, Henan Province using with ERT. The top of the wall remains were located at 2–4 m depth with a bottom 10–12 m deep. These great depths were caused by frequent flooding and diversion of the Yellow River at the site. A MCOHM-21 resistivity-meter system was used to acquire the data. The ERT results indicated that the apparent resistivity of the rammed soil layer was about 35–42 Ωm, while the apparent resistivity of the surrounding soil was about 15–25 Ωm. A similar ERT survey, performed with a DUK-2 resistivity-meter system, was carried out at the archaeological site of Sanxingdui Ancient Ruins, a very famous Neolithic-Bronze Age site located in the Southwest China (Su et al., 2007).

Moreover, the near-surface geophysical group from Zhejiang University has carried out a large number of experimental surveys at the Liangzhu site in recent years (e.g. Zhao et al., 2015b). This is a famous Neolithic site that was the centre of jade culture centre in south-east China. The buried remains of the ~40–60 m wide rammed earth ancient wall at the Liangzhu site, were discovered in 2007 (Zhejiang Institute of Cultural Relics and Archaeology, 2008). Figure 2 provides two examples of geophysical results around the wall, i.e. an ERT survey results showing the north wall. This was generated from 24 parallel ERT survey lines and a magnetometer survey map outside the east wall, performed with a Benteng resistivity-meter system and a Caesium optical pumped magnetometer G858, respectively. The continuous high resistance, associated with the rammed earth remains underground, is cut off by the low resistance part, which can be inferred as the location of the gate in the Liangzhu Period, besides, the continuous low resistance is associated with the water system, validated by drillings. In addition, the anomalies in the magnetometer survey map are associated with the distribution of cultural accumulations during the Liangzhu Period, which are roughly the same as the drilling results.

Fig. 2

The location of study area at Liangzhu site, Hangzhou, the ERT map of about 1.5 m depth acquired at the north wall and the magnetic map acquired outside the east wall

3.2 Ancient Tombs

Ancient tombs (burial mounds) with individual or collective funeral chambers have worldwide distributions. Such kind of detection objects is one of the most important archaeological interests, as they may contain important findings of great historical and economical values and they have great archaeological significance. However, the characterisation of burial mounds is an especially challenging geophysical problem, due to uneven topographical terrain, complicated surface environment, and complex distributions of the burial archaeological features (e.g. Dai & Xie, 2015; Zhao et al., 2019). Archaeo-geophysical characterisation at the Mausoleum of Qinshihuang was carried out combining different methods and this survey strategy has also been used at other burial sites such as the noble tomb of Chu State during the Spring and Autumn Period (Zhang, 1996), the cemetery of Marquis Haihun of the Han dynasty (Li et al., 2021), and masonry family tomb during the Han and Wei Period (Zhang, 1999b). Figure 3 shows the ERT result of the survey conducted at the burial mound of Hepu Han in South China were ~1200 tombs were excavated by archaeologist since the 1950s (Chen et al., 2018). A Trimble 5800 RTK-GPS was carried out to obtain high-resolution Digital Elevation Models (DEMs), while a Geopen E60D resistivity-meter system was used to acquire the ERT data. The iso-resistivity surfaces can emphasise temporal and spatial variations in data volumes, and detailed features such as tomb passage, robbing hole, brick facade, archway, chamber, rear chamber, and two side rooms were characterised obviously and effectively.

Fig. 3

The location of ERT example at the Hepu Han Tombs, the grid of 18 profiles overlapped on the digital elevation map, and the ‘pseudo-3D’ interpretation of the burial mound. (Adapted from Chen et al., 2018)

3.3 Cultural Heritage Protection

Geophysical methods can be used to evaluate states of cultural heritage structures such as grottoes, stone carvings, and murals (e.g. Lu et al., 2020). There are obvious physical differences between weathered rock vs un-weathered rock, and strongly weathered rock vs weakly weathered rock. Besides, the original resistivity/dielectric constant of the rock can change after anti-weathering coating liquid penetrates the repaired cultural heritage. Therefore, GPR and ERT have been used to assess the efficacy of rehabilitation of cultural heritage, as well as weathered interface and in-fill of cracks/voids, although such geophysical applications are still very limited in China. Figure 4 provides an inspection example of Leshan Giant Buddha with 71 m high, the tallest Buddha in the world (Zhong, 2002). The geophysical surveys were performed by the Research Institute of Railways in the 1990s. The result is an interesting plane contour of moisture content on the face of the Buddha. Although the author mentioned that resistivity and sonic methods were used, unfortunately, he did not describe the specific process of how to get the final result. Besides providing the plane contour of moisture content, the author only mentioned that their results can locate the potential cracks and the weathering depth of the statue subjectively.

Fig. 4

The photograph (from Miss Suyu Qian) and the plane contour of moisture content on the face of the Leshan Giant Buddha. (Adapted from Zhong, 2002)

3.4 Urban Underground Remains

When ancient remains are buried underground in modern cities (e.g. Gan & Yao, 2021; Zhang & Wang, 2021), commonly used magnetic, electromagnetic and shallow seismic methods are ineffective due to the interference of a large amount of environmental noise. Moreover, the dense asphalt road network and hard cement ground make the traditional ERT with plug-in electrodes become unrealistic. In such case, besides GPR (e.g. Science and Technology Archaeology Centre, Institute of Archaeology, Chinese Academy of Social Sciences, and Qicheng Cultural Relics Scenic Area Management Office, 2017), more new technologies such as capacitive-coupled resistivity method need to be considered in the urban site. Figure 5 provides inversion results of two survey lines performed with an OhmMapper TR2 capacitive-coupled geo-electrical mapping system in the city centre of Hangzhou (Bie et al., 2017), where the high resistivity values are associated with the buried seawalls, built with blocks or stones to resist tides and waves during the Wu-Yue Kingdom period (about 910 AD), which are widely distributed in the southeast coastal area of ancient China.

Fig. 5

The schematic diagram of capacitive-coupled resistivity system, the inversion results of two survey lines performed in the city centre of Hangzhou, and the photograph of the excavation for verification. (Adapted from Bie et al., 2017)

3.5 Underwater Archaeology

The underwater investigations of antiquities, ancient ruins, and ancient tombs, attract strong attentions from archaeological experts and public, with its unique cultural charm. It’s difficult to perform underwater archaeological surveys only by divers, geophysical explorations are more and more important, especially with the gradual improvement of marine equipment. Due to the different working environments between underwater and land, particularly influenced by the underwater visibility and currents, archaeo-geophysical methods on water are totally different and are used as follows: side-scan sonar, magnetometer for water use, multi-beam sounding system, sub-bottom profiler and GPR (e.g. Yang, 2014; Hu et al., 2016; Ma et al., 2016; Qin et al., 2018), equipped with diving equipment and corresponding logistical supports. The investigations of ancient shipwrecks, including wooden ships and ironclad warships (e.g. Wei, 2008; Zhou, 2020), have provided rich cultural relics for the study of ancient Chinese social history, greatly promoting the research of ancient Maritime Silk Road and the dynamic process of overseas trade history and relationship history (e.g. Underwater Archaeology Research Centre, National Museum of China, and Ningbo Institute of Cultural Relics and Archaeology, Zhejiang Province, 2020). As previously mentioned, integrated geophysical methods were used to detect ancient shipwrecks underwater in the sea of Liaoning Province as early as 1991, besides, more ancient shipwreck detections have been performed since then, like the No. 1 shipwreck of Pingtan Wanjiao from Qing Dynasty, in the East China Sea, the No. 1 shipwreck of Huaguangjiao from Song Dynasty, in the Paracels, and the No. 1 shipwreck of Nan’ao from Ming Dynasty (e.g. Yang, 2014; Ma et al., 2016).

Moreover, underwater archaeology in China has also some applications on rivers and lakes, for example, Yu et al. (2009) detected the distribution of famous buried-silver site in the Minjiang River with ERT, hidden here by Zhang Xianzhong, the peasant rebel leader of the Daxi Army in the late Ming Dynasty, which were recorded by many documents (e.g. the historical documents Shubi and Shunanjishi, both written in Qing Dynasty), and Qin et al. (2018) investigated underwater cultural relics of Yue kiln buried beneath Shanglinhu Lake, Zhejiang Province with GPR. Figure 6 provides a 3-D imaging of underwater ancient city, acquired with Simrad EM 3000 multi-beam sounding system on the Qiandao Lake, Zhejiang Province (Liu et al., 2005). The ancient city (i.e. the Suian County, also called Lion city) was submerged in the lake water due to the construction of Xin’anjiang Hydropower Station in 1959. As can be seen from the figure, the ancient city walls, streets and buildings are clearly displayed, providing preliminary quantitative information for the research and protection of the underwater ancient city.

Fig. 6

Photographs above (2019, from the first author) and below (from the website of Chinese National Geography, 2009) the Qiandao Lake, and a 3-D imaging of underwater ancient city, acquired with Simrad EM 3000. (Adapted from Liu et al., 2005)

4 Conclusions

Archaeo-geophysics can accurately identify, image and map the spatial extension of near-surface archaeological features or changes in the matrix of a site, so they are recommended as valid methods to optimise location and design of excavations. Throughout the past 70 years, researchers and practitioners witnessed the rapid development of geophysics in the field of Chinese Archaeology. This chapter has shown the historical development of the discipline of archaeo-geophysics, as well as some successful case studies in China which reached the peer reviewed literature. These included ancient city sites and ancillary building remains, ancient tombs, cultural heritage protection, urban underground remains, and underwater archaeology. However, failure is normal in reality. Our experiences suggest that failing to meet expectation is far more common than the successes reported. This observation is common for all near-surface geophysical applications and not restricted to archaeological prospection.

Without any doubt, geophysical methods are progressing from traditional location and experimental surveys in small scale to detailed imaging and diagnosis nowadays. However, interpretation of both 2D and 3D data are highly subjective and depend greatly on the user experience and understanding. Objective guidelines for survey data collection and data imaging are yet to be further explored in China. This work should involve preliminary available synchronous archaeological information as much as possible.

The development has paved the way to large-scale and regular use of the geophysical methods in almost all types of potential archaeological sites in future. Of course, we have to acknowledge that visual inspections via excavations and drilling cores are still the most common methods to reveal the truth on filed archaeology at present in China. It is probably not because of the unavailability or unpopularity of the geophysical methods, but the lack of necessary awareness between traditional field archaeologists. Given the large increase of wider applications, we stay positive with the development so far and expect a much wider use of geophysical methods on Chinese field archaeology in future.