The Place of Archaeo-Geophysics in Archaeological and Cultural Heritage Site Investigations in Turkey

Abstract

The first examples of archaeo-geophysical investigations in the territory of Turkey, are seen in the 1960s. Archaeo-geophysical studies, which came to an important place in archaeological site investigations and documentation of cultural heritage sites after the 1990s, have taken place in many legislations in the country today. Recently, the employment of non-destructive geophysical techniques in Turkey’s archaeological sites has been drastically increasing. This chapter presents the history of archaeo-geophysical studies, methodological developments, educational and commercial advances. Additionally, widespread commercial applications, how archaeological site types are handled, verification of the relationship between geophysics and excavation results, and good practice examples are also summarised. In addition to the soil variations encountered in archaeological sites, the interpretation of the results of the geophysical techniques used in the determination of the archaeological context, which is highly complex due to ancient earthquakes in archaeological sites in Turkey, is also discussed in this chapter. Although archaeo-geophysics is an essential part of the study of archaeological and cultural heritage sites in Turkey, soil prospecting is limited and there appears to be a lack of integration in comparing geophysical results with the soil prospecting results.

1 Introduction

The land of Turkey has contained various archaeological settlements since the Palaeolithic age. The overall stages of evolution of the last hunters-gatherers that are thought to be in the transition phase to agricultural activity and animal husbandry were clearly observed in the archaeological excavations conducted in the south-eastern part of Anatolia in Turkey. Recently, it has become clear that an uninterrupted transition has been observed from the cultic centres of the first settlements of the Epipalaeolithic age towards the settlements of the Pre-Pottery Neolithic (PPN) age (Özkaya, 2009; Asouti & Fuller, 2012; Asouti, 2017; Boyd, 2018; Kodaş et al., 2020). Thus, with the emergence of Göbeklitepe and similar settlements (Karahantepe, Nevali Çori, Hallam Çemi, etc.), all phases of human evolution from the Epipaleolithic to the Neolithic period (from 11,500 BC to 8000 BC) became identifiable in this region. Furthermore, many cities in today’s Turkey contain extensive archaeological remains from the Neolithic period to the Ottoman period.

The Anatolia have been inhabited by various civilisations since the Epipaleolithic ages and thus have various settlement patterns. They start from the first settlements on the rock shelters in the Epipalaeolithic age, moving to the formation of the first cities that emerged in the höyüks (tell or multi-layered settlement) and from there to the emergence of organised urban centres. Thus, there are highly variable settings spanning from single-layer settlements covering large areas to multi-layered settlements. In addition to these, the existence of very different cultures reveals diversity in grave and cemetery customs.

The land of Turkey consists of different geological formations. Particularly, this geography, whose lands were formed during the Neotectonic period, was also exposed to major tectonic effects from the Quaternary and Holocene. These features cause very different soil types to be seen in terms of archaeological settlement. The wealth of natural resources has supported the long-term settlement in the region. However, active tectonic effects and different geomorphological events cause various soil characteristics to emerge in areas where archaeological sites are located, and thus different soil types cover the archaeological context. This situation may have complex effects on the data obtained from geophysical investigations. Thus, the soil effect that directly controls the success of geophysical methods could cause different results and success rates of the geophysical prospection. The fact that many settlements are exposed to earthquake effects, especially because of active tectonics, causes further complexity of the archaeological context. This situation results in a more complex image of geophysical data, as the complexity in the buried archaeological context affected by earthquakes causes lateral or vertical displacements with depth changes. Thus, important difficulties arise during the archaeological interpretation made from the geophysical data.

The Anatolian soils have an important place in testing the results of the methodologies applied in archaeo-geophysical studies. However, the soil prospecting studies conducted on Anatolian archaeological sites are limited (Dirix et al., 2013). Particularly, the semi-arid climate conditions in the summer period and thus the excessive drying of the soil is an important problem for methods directly sensitive to soil variations such as resistivity. Additionally, large erosion episodes in the soil can cause the archaeological cultural layers to be buried very deep. This situation complicates the usage of many methods and even prevents their implementation. The intensity of seismic activity causes various damage to the archaeological settlements coming from different periods. Since this situation will significantly mix the archaeological features in the buried context, it will cause much more complex geophysical results obtained than simply when an archaeological context is buried within a heterogeneous soil matrix. Horizontal and vertical displacements that occur on the walls of buried structures, especially after large earthquakes, make this situation even more dire. Apart from these, intense treasure hunting activities are another important problem for geophysical studies. Due to these factors, as soil content is significantly mixed, it ultimately decreases the success of geophysical methods. As a result, it will be important to determine the soil properties and characteristics in detail before any geophysical study. Additionally, changes in soil character and differences in buried depths will also be important in choosing the methodology to be used.

The first examples of archaeo-geophysical applications in Turkey were carried out on the tumuli of Karnıyarık Tepe (Manisa) and Nemrut Dağ (Adıyaman) in the early 1960s (Hanfmann, 1965; Goell, 1968, 1969). Especially after the 1970s, the more frequent application of geophysical methods by foreign excavation teams conducting research in Turkey and the emergence of positive results increased the usage of the methods. Within the scope of these studies, magnetometer surveys in researching some burial grounds and especially the höyük and some antique city investigations came to prominent. Additionally, the first resistivity studies conducted in limited areas by Turkish researchers during the Keban dam studies in the summer of 1968 are commendable in this regard (Yaramancı, 1970). The widespread use of archaeo-geophysical investigations in Turkey started in the late 1980s and continued until the 1990s, increasing the interest in their application (Drahor, 2011a). However, the main development emerged at the beginning of the 2000s and is still increasingly continuing today. Especially in the last decade, with the introduction of application techniques into legal regulations, the tendency of private companies to apply such applications has increased to a great extent. In this process, another important development was that the applications extend to the documentation of preservation of the cultural heritage sites apart from archaeological sites.

Starting from the beginning of the 1990s, doctorate, and master’s theses conducted on the methodological development of geophysical methods used in archaeological fields were also beginning to appear. The positivity of the results of these studies allowed the increase in the projects on the subject and the usability of different techniques. The results of these studies were published in many international journals and books and started to appear in literature.

Today, ground-penetrating radar (GPR), magnetic gradiometry (hereafter magnetometry) and electrical resistivity applications are among the commonly used geophysical techniques in Turkey. In particular, researchers working at universities generally apply integrated techniques, while the private sector commonly uses GPR techniques, with some exceptions.

2 The Archaeo-Geophysical Research in Turkey and Its Impact Upon Education, Methodology and Commercial Application

The first archaeo-geophysical studies primarily focused on investigating the different fields with selected geophysical techniques and testing the success of these techniques applied (Drahor, 2011a). Later, archaeo-geophysics played an important role in Turkish archaeology using methodological advances, detailed scientific studies and multiple method trials. Because of the developments in legal procedures, especially in the protection of archaeological and cultural heritage sites, archaeo-geophysical applications have been used more effectively. Thus, the private sector applications in archaeo-geophysics were initiated and have increased extensively in the last decade.

2.1 Brief History

The first geophysical study in Turkey was conducted by American geophysicists on Nemrut dağ tumulus between 1963 and 1964 (Goell, 1968, 1969). The aim of Goell, who was the excavation team leader, was to determine the burial tomb of Antiochus I (69–36 BC), the king of Commagene. The next investigation was conducted in 1963 on Karnıyarık tepe, another important tumulus in Anatolia, to find the tomb of Giges, which was the first king of the Mermnad dynasty of Lydia. In this study, American geophysicists conducted vertical electrical resistivity sounding (VES) studies on the tumulus (Hanfmann, 1965). The first geophysical study was carried out by a team of Turkish academicians led by A. Yaramancı from İstanbul University as a part of the Keban Dam Rescue Project in 1968. In these studies, electrical resistivity profiling measurements were attempted in a limited part of the Ağın, Tepecik, and Norşuntepe höyüks, respectively (Yaramancı, 1970). After the first studies, systematic and multi-methodological investigations were carried out between 1970 and 2000 on flat settlements and höyük’s (multi-layered settlement), especially to reveal settlement plans and important structures (Demircihöyük (1977), Boğazköy-Ḫattuša (1980), Hassek Höyük (1981), Halikarnassos (1988), Göltepe (1991–1992), Truva (1992), Acemhöyük (1992–1994), Metropolis (1992–1994), Çatalhöyük (1992–1993), Kerkenes (1993–2010), Miletos (1995–1996; 2003–2009), Ziyaret Tepe (1998–2004) (Becker, 1979, 1980, 1981; Becker et al., 1993; Drahor, 1993a, b, c, d, 1994a, b, 2021; Shell, 1996; Matney & Donkin, 2006; Çayırezmez et al., 2008; Summers et al., 2010; Brückner et al., 2014)). Additionally, geophysical studies were conducted between 1989 and 1994 to determine the locations of different pottery production workshop sites (Reşadiye, Hisarönü, Sinop, Gaziköy-Hoşköy) in Anatolia (Hesse, 1992; Drahor et al., 1995). Geophysical investigations were also carried out in Nemrut dağ (1989), Çiftlikkırı (1991), Argavlı (1992), Kösemtuğ (1992), Kepirtepe (1992) and Karnıyarık tepe (1993) tumulus by Turkish and foreign geophysicists at the beginning of the 1990s (Şahin, 1992; Başokur, 1993; Drahor, 1993f, 1994b; Greenewalt, 1995; Pınar & Akçığ, 1997). Many large-scale and integrated systematical geophysical investigations continued in different archaeological sites in Anatolia between 1990 and 2021. The most important examples are: Kerkenes (1993–2010), Sardis (2001, 2018–2021), Zeugma (2001–2006), Sarissa (2000–2004), Šapinuwa (2012–2019), Burgaz (1998–2007), Troia (1992–1994), Ephesos (1998–2014) Miletos (1995–2011) (Summers et al., 2010; Drahor, 2006; Drahor et al., 2007, 2008, 2015; Çayırezmez et al., 2008; Erkul et al., 2008; Seren & Ladstatter, 2011; Brückner et al., 2014). Furthermore, various magnetometer and resistivity-meter systems were tested and developed during such studies (Faßbinder, 2011 and references therein; Summers & Summers, 2012).

2.2 Methodological Developments and Academic Advances

Geophysical studies conducted in Anatolia brought some instrumental developments. One of them was the development and establishment of the Bavarian magnetometer system. In these studies, proton, caesium and CS2-system magnetometers were tested in some archaeological sites (Demircihöyük-1977, Troia-1992 and 1994, Aşağıpınar-1994, Pompeipolis-2007). Kerkenes geophysical studies were conducted using Geoscan’s RM15 soil resistance meter system. However, the extremely dry soil conditions during the summer period revealed some measurement problems. As a result, a system was developed to improve data collection in such environments (Çayırezmez et al., 2008). During this time, some methodological developments and novel application examples have emerged in self-potential application, electromagnetic VLF (very low frequency), Electrical Resistivity Tomography (ERT) for multi-layered sites, and magnetometer surveys for indoor applications (Drahor, 2004; Drahor et al., 2011; Berge & Drahor, 2011a, b).

When the academic past of archaeo-geophysics in Turkey is examined, contrary to the increasing geophysical investigations in the field of archaeology, it seems that it has not been sufficiently developed. In fact, many geophysical studies of archaeological sites have been carried out by local researchers working at universities in the last decade. However, when the scientific background of the studies is examined, it is revealed that many of them are scientifically insufficient to investigate the true archaeological context. The first scientific study on archaeo-geophysics in Turkey was the doctoral thesis conducted by Mahmut Göktuğ Drahor in 1993 (Drahor, 1993e). In the following years, ~ten other doctoral theses paid attention to this subject to some extent. These include two theses that examine specific geophysical method(s) but only with a section devoted to the application of such methods in archaeology. Generally, it seems that a significant part of doctoral theses does not adequately describe the archaeological context investigated and the methodological approaches are insufficient. Additionally, the majority focuses on the application of similar methodological practices to various archaeological sites. Master’s theses (52 in total) have similar characteristics. There is an increase in the number of these theses from 1993 to 2007, and after this date, except for 2 years (2011 and 2019), there is a decrease in postgraduate theses (Fig. 1a). The ratio of postgraduate theses conducted on archaeo-geophysics at the departments of geophysical engineering on all postgraduate theses on geophysics is 4.2%. Therefore, it seems that there is still not enough interest in the subject in Turkey, which has a rich archaeological heritage. While magnetometry, electrical resistivity and GPR methods are at the forefront as these topics, other methods, or their combined used, have been little explored (Fig. 1b). When the courses given in universities related to the subject are examined, it is revealed that 15 courses have been opened on this subject so far, eight of them still active. Ultimately, all of them have the status of elective courses. To increase interest in the method, develop methodologies, and train students, the Research and Application Center for Near Surface Geophysics and Archaeological Prospection (CNSGAP) (2004–2020) was established under the leadership of Prof. Dr. Mahmut Göktuğ Drahor, affiliated of Dokuz Eylül University. During its activities within 16 years, the Center has contributed to many scientific and technological developments on near-surface and archaeo-geophysical research by addressing novel theoretical and practical research topics. Additionally, the Center has organised vocational training programs, meetings, symposiums, and similar events to develop scientific and technical knowledge on near-surface geophysics and archaeological prospection studies. One of them is the 9th International Conference on Archaeological Prospection (https://www.archprospection.org/archpros11) held in Izmir between 19 and 24 September 2011. Apart from this, the Chamber of Geophysical Engineers of Turkey has also organised some courses and training programs related to this subject.

Fig. 1

(a) Number of postgraduate theses on archaeo-geophysics between 1993 and 2021. (b) Distribution of geophysical methods used in postgraduate thesis conducted on archaeo-geophysics in Turkey (GPR: ground-penetrating radar, SP: self-potential, EM: electromagnetic, VLF: very low frequency). (c) Active tectonic map of Turkey. The locations of the study areas associated with this chapter are overlaid on the map. (Faults are taken from Şengör et al., 1985; Bozkurt, 2001; Koçyiğit, 2003; Emre et al., 2013)

2.3 Commercial Applications in Archaeo-Geophysics and Its Impacts

Long-term agricultural activities, rapid urbanisation, industrialisation, dam-highway-railway constructions, and mining, as well as human activities such as treasure hunting, have created a negative impact on the archaeological and cultural heritage sites in Turkey. In this extremely fast process, the importance of archaeo-geophysical studies in documenting Turkey’s cultural heritage is undoubtedly great. However, due to the lack of sufficient academic experts on the subject and the limited number of studies, the demand from society could not be met. The fact that it has not also an official organisation established on this subject ultimately led the private sector to show interest in this issue. The increase in interest over this subject, when considered together with the development of Turkey, led to the establishment of new companies dealing with the topic of archaeo-geophysics. Most of the private sector working on archaeo-geophysics performs only GPR surveys (aka georadar). For this reason, it seems that the term “geophysics” equals “georadar” in the administrative jargon of conservation boards and other organisations of the “Ministry of Culture and Tourism”. GPR has become prominent and there has been a false perception as if it is another application different from geophysics. Based on these statements, there is a misperception among different regulatory bodies that simply conducting GPR surveys is enough to evaluate sites under development. Geophysical surveys combining different techniques are rarely considered by the private sector. On the other hand, the interest of excavation groups in subcontracting geophysical services is increasing. GPR applications are pursued in restoration and infrastructure services as per the regulations. Integrated (or combined) geophysical surveys carried out by the private sector have demonstrated potential in major highway, railway, port, pipeline and metro constructions. However, note that soil prospection is not considered in private sector applications.

3 The Place of Geophysics in the Preservation of Cultural Heritage

The place of geophysical studies is undoubtedly critical in the investigation and protection of many religious buildings, caravanserais, castles, sanctuaries and restored cultural monuments. The increase in public investment in Turkey in the last decade has directly affected the archaeological and cultural heritage sites. Especially, the development of social awareness has also increased the interest of the community in cultural heritage. Depending on these facts, intensive restoration works emerged in the process and the state provided significant financial support. Additionally, financial aid from the European Union funds contributed to the acceleration of the restoration work. Thus, restoration works in many cultural heritage sites and structures, especially religious ones, were accelerated. Naturally, the need for high-resolution geophysical studies, as a non-destructive approach, has emerged in these studies. Today, extensive GPR surveys are conducted especially on the structural elements of the interiors of buildings that are still standing, such as walls, floors and domes. Thus, in addition to the structural features of the investigated buildings, other unknown features (such as an unknown crypt) have also been revealed. Some investigations on this subject carried out in Hagia Sophia (İstanbul) are admirable (Yılmaz, 2013; Moropoulou et al., 2013; Barba et al., 2018). As a result, although the GPR method is widely used in the conservation and restoration studies of cultural heritage sites in Turkey, electrical resistivity tomography (ERT), seismic and magnetometer surveys have also demonstrated their potential (Drahor et al., 2011).

4 On the Valid Planning of Geophysical Investigations in Turkey Where Highly Variable Earth Indicators Exist

The significant earth changes and climatic differences seen in Turkey have great importance in the correct interpretation of geophysical data and its successful results. As it is known, correct planning should be made by considering these features before starting archaeo-geophysical investigations in areas where archaeological site type, soil characteristics, geomorphological effects and tectonic regimes are more variable and active. The Turkish territory is one of the most active areas in the world in terms of tectonics. This is revealed by the existence of many active faults in the country. The activity of a fault depends on the frequency of earthquake recurrence intervals on that fault. In particular, the activity within the Quaternary allows it to be classified as an active fault. Since palaeo and archaeo-seismological studies better reveal the activities in the Holocene period, the activities of this period are better known in Anatolia, especially. The general active tectonic fault map of Turkey has been created with the geological and geomorphological investigations carried out on the faults by the General Directorate of Mineral Research and Exploration (MTA) (Fig. 1c). Unfortunately, many archaeological settlements in Anatolia were established in areas near these faults and these faults had a great impact on their preservation. During the excavations in Anatolia, significant destructions are encountered in the archaeological settlements located near the active fault zones. Vertical displacements occurring in subsurface structures pose an important problem for geophysical investigations. In fact, the archaeological context of the same layer, in which displacements of up to 0.5 m are observed, can be found at different depths. This situation particularly affects GPR studies, which are interpreted as time/depth slices. Thus, GPR time/depth slices, which are thought to be taken from the same depth, extend at different depths due to deformed structural elements and cause problems in their interpretation. Before performing time/depth slice studies in such areas, a detailed analysis should be made on the processed radargrams (B-scan or reflection profiles) and it should be determined whether such a situation exists. Additionally, the archaeological context can be covered with a thick soil cover due to the old landslides, soil-debris flows, and vertical displacements result in active faulting. This situation causes significant mixing in the soil content and hinders the success of geophysical methods in determining buried archaeological structures. When the agricultural activities of recent years are added to this, a common soil erosion phenomenon is encountered in Turkey. Field types have a significant impact on geophysical investigations as well. While the PPN settlements of Anatolia are generally seen as single or multi-layered settlements on the bedrock, the Neolithic age settlements in the plains are generally multi-layered and have also very different variability in terms of size. This situation eventually leads to the formation of mounds reaching a height of about 20–25 m (Berge & Drahor, 2011a, b). Obviously, these two types of settlements are difficult areas for investigation in terms of geophysical studies, due to reasons such as the multi-layered nature of such areas, the overlapping of different archaeological layers and the bedrock effect. In particular, mono-layered and laterally spreading areas, such as Classical, Hellenistic, and Roman settlements, are better targets for geophysical investigations. However, note that the application of integrated methods would yield more useful results in cases of mono-layered settlements covered with thick alluvial or colluvial layers.

The majority of archaeological sites in Anatolia are found inside alluvial basins, and the composition of the basins consists of dense layers of clay, silt, and in some places, sandy layers, which has a significant impact on geophysical exploration. Additionally, shallow groundwater levels are another problem during geophysical studies. Apart from these, difficulties may arise in terms of electrical studies because a significant part of Anatolia has a semi-arid climatic feature and therefore the soil conditions are very dry, especially in the summer period. Furthermore, intense burned zones are encountered in the Neolithic, Bronze, and Iron Age layers. The extensive fires that make up these zones cause the archaeological context to undergo significant physical and chemical changes. As a result, before starting the geophysical studies, such problems should be thoroughly examined to decide on the method to be applied. Although magnetometer surveys, which are generally used in geophysical studies, have some problems, they generally give satisfactory results. However, the results of magnetometer surveys can be complex because of the multi-layered settlement context in the höyük areas. In electrical resistivity studies, despite excessive drying of soil conditions in summer, the problem can be solved by the emergence of advanced devices in terms of controlling the contact resistances and signal/noise ratio, and choosing a less sensitive configuration to such noise (Schmidt et al., 2020). Additionally, with the tomographic application of resistivity, it was possible to obtain models that gave excellent results and contributed greatly to the interpretation. Since GPR methods are particularly affected by dielectric permittivity and electrical conductivity, they can produce inadequate results in areas with clayey environments, near-surface groundwater, earthquake deformations, and thick colluvial cover. It should also be noted that self-potential, seismic, and induced polarisation methods can yield important results in höyük, mining-metallurgical settlements, and grave investigations (Drahor et al., 1996, 2015; Drahor, 2004).

5 Selected Field Examples Depending on the Type of Archaeological Site

In this section, the results of six different cases of multi-layered, mono-layered, grave, cultural heritage conservation and restoration studies in Turkey are presented. Two of them were selected from Western Anatolia, two from Central Anatolia and two from South-eastern Anatolia. Locations of these study areas are near the tectonically active regions (Fig. 1c).

5.1 Multi-layered Settlements

5.1.1 Acemhöyük Archaeological Site

Cases representing multi-layered settlements were selected from two different regions. The first is Acemhöyük, one of the great höyüks of Central Anatolia, which remains from the Assyrian Trade Colonies. Acemhöyük extends to 700 m in east-west direction and 600 m in north-south direction. The top of the höyük is flat and its highest point is 20 m. Excavations revealed that the shallow cultural layer was built with a regular urban orientation (NE-SW 45° and NW-SE 45°). The city is located 10 km southwest of the Tuz Gölü Fault Zone (TGFZ), an important active fault in Central Anatolia. The fault zone is a normal fault with an NW trend and active oblique slip. The settlement, which is close to the Tuz Gölü, was built on a Holocene alluvial environment (Fig. 1c). Excavations at the site began in 1962, and although there is evidence that the first settlement began at least in the Early Bronze Age (3000 BC), the most prosperous period of the settlements was during the Assyrian Trade Colonies (2000–1750 BC). Dendrochronology studies determined that the city was destroyed because of an extensive fire in about 1789 ± 50 BC. After this period, the settlement on the höyük ended and only some parts were resettled again in the Early Hellenistic period. This settlement continued until the third century AD. Because of the great fire in the Assyrian Trade Colony period, the mud brick walls of the buildings have undergone a significant physical and chemical change. In particular, mudbrick walls, which normally do not have magnetic properties, have obtained increased magnetic properties due to the thermo-remanent magnetisation that occurred because of this fire. Resistivity, self-potential, magnetometry and EM-VLF studies were conducted in this area between 1992 and 1994 (Drahor, 1994a, 2004; Drahor et al., 1996, 1999; Drahor & Kaya, 2000). An example of the results of the magnetometer surveys at these studies is given in Fig. 2a. In this study, data were collected using a Geometrics G-856 proton magnetometer that measures the total magnetic field of the earth. The sensors were held at 60 and 180 cm heights and data were obtained using the vertical gradient measurement. In the total magnetic field and gradient data, the values were very high on heavily burnt areas, walls, and other archaeological features. Corrected data were processed with different signal and image analysis techniques to obtain the most suitable images. The result of the magnetometer survey (after the inverse filter application) conducted in 1994 in the area between two different palaces (Hatipler and Sarıkaya) excavated in the 1960s and 1970s, is given in Fig. 2a. The presence of a good contrast between the traces of the burnt building elements and the soil is seen in the image. The shape of the buildings in the south is very distinctive and the amplitudes of the magnetic traces formed due to combustion on the mudbrick walls are clearly visible depending on the burning intensity. An archaeological excavation was conducted to verify the results of the magnetometer survey. The revealed structure, which was buried close to the surface, extended to a depth of 2 m. At its base, there were large burned wooden beams that went down to the floor due to a large fire (Fig. 2a, photographs given in the right-hand side). As a result of the excavations that continued in the same area in the following years, the existence of an important building complex was revealed.

Fig. 2

(a) Results of the magnetometer survey and excavation photographs obtained from Acemhöyük archaeological site in Aksaray. (Modified from Drahor & Kaya, 2000). (b) GPR depth slices and reflection profiles obtained from Sardis archaeological site in Manisa. (Modified from Geoim Ltd., 2020)

5.1.2 Sardis Archaeological Site

The second example of a multi-layered archaeological settlement was selected from the Sardis area, which was the capital of the Lydian located in Western Anatolia. Sardis is located on the banks of the Paktolos River and approximately 2 miles south of the Hermus River, and it was founded on a hill on the banks of the Hermus River in the Early Lydian period (eighth century BC). Sardis, which was the last stop of the famous King Road starting from Susa, was very important in the Roman period. The city, which excessively grew during this period, spread towards the plain below. Sardis was founded on the fault scarp of the Gediz Graben, formed by east-west faults in Western Anatolia (Fig. 1c). The city has been under the influence of many earthquakes in ancient times. Since earthquakes in this region generally occurred at shallow depths, they caused significant damage to the stone structures of the settlement. The largest earthquake ever seen in Sardis occurred in AD 17. The earthquakes in the seventh and thirteenth centuries AD also caused serious damage to the Lydian city, which was built on a weak Pliocene Sart formation composed of semi-consolidated conglomerate and sandstone materials. Additionally, the city was covered with a thick soil layer because of landslides caused by major earthquakes and soil flows caused by large erosion episodes. For this reason, it is impossible to observe any traces of structures from the early periods, except for some Roman and Byzantine structures on the surface. In the upper parts of the city, there is a thick cultural filling starting from the Early Lydian at the bottom and following the Lydian, Persian satrapy, Hellenistic, Roman and Byzantine periods. Lydian strata are buried at a depth of 7–8 m, and sometimes at a depth of more than 10 m. As a result, integrated geophysical methods are required to detect these layers. For this purpose, an integrated geophysical survey including magnetometry, ERT, VLF-resistivity, and seismic methods was conducted in Area 55 in 2001 (Drahor, 2006). As a result of these studies, Roman and Byzantine layers buried close to the surface were mapped. Since the lower layers of these structures, where significant structural deformations were observed because of major earthquakes, were not excavated, any data related to the Lydian period could not be obtained. Additionally, integrated, and large-scale geophysical studies were carried out in 2018 and 2019, in Area 49 and its surroundings, and in Area 55 and its surroundings in 2021 (Geoim Ltd., 2020). In these studies, GPR, ERT, induced polarisation tomography (IPT), seismic refraction P tomography (SRT), and multi-channel surface wave tomography (MASWT) methods were applied. In Fig. 2b, some results of the GPR investigations conducted in Area-49 and its surroundings are given. The traces of buried archaeological structures can be observed with high radar reflection amplitudes at the depth slice obtained from 1.44 to 2.47 m. The fact that the traces of the buildings have two different orientations suggests that two different settlements may have been buried at this depth. It is thought that almost N-S and E-W directional extensions are seen in the west of the area may be related to the Roman layer, and the traces extending in NW-SE and NE-SW directions in the north-eastern part of the area may be related to the possible Lydia layer. It also comes to mind that the density of the complex traces in the southern section may indicate the talus fillings formed due to earthquake-induced landslides. The images obtained from five different depth levels of the NW-SE and NE-SW oriented structure within the area surrounded by the square frame are given in the middle part of the figure. The traces of the structures here are clearly visible at three depth levels between 0.42 and 2.9 m. The radar reflection contrasts between soil and structures are quite good, and therefore the structures appear distinctly. It is interpreted that the mixed reflections in the south-western part of the large building may be due to an earthquake-related episode. Interpretations of five separate reflection profiles selected from this area are given above them. Although the traces of the structures are seen in the reflection profiles, the presence of a westward slope is mostly observed in the traces. Additionally, the changes related to the deformation in the reflection traces of the walls and interiors of the structures reveal that the layers here may have suffered significant damage because of an earthquake. When the relationship between the lossy zones indicated by “L” in the figure and the traces of structures is studied, we could suggest that a fill due to sloping slips may cover the archaeological layers.

5.2 Mono-layered Settlements

5.2.1 Šapinuwa Archaeological Site

A good example of mono-layered archaeological sites is Šapinuwa, a Hittite imperial city located on a plateau west of the Çekerek River in the Central Anatolia, surrounded on three sides by deep valleys (Fig. 1c). The foundation of the city is dated to 1400 BC, which corresponds to the Middle Kingdom period of the Hittite Empire. Šapinuwa was a religious, military, and governmental centre and had close links with Ḫattuša, the capital of the Hittite Empire. Archaeological finds have shown that the city had a sacred area where religious rituals were held during the Hittite period and that the city functioned as an important cultic centre. The city consists of two separate parts, namely Tepelerarası and Ağılönü. One of these, Tepelerarası is a residential area of an aristocratic class, while Ağılönü is a sacred area used for different religious rituals. During the excavations in the Tepelerarası area, an important archive containing more than 4000 clay cuneiform tablets in an official building was found. As a result of the excavations made in the area and readings of some cuneiform tablets, it is understood that the city consists of sacred areas, palace, military base, official buildings, and other important structures (Süel, 1995). Šapinuwa is located between the Sungurlu fault zone (SFZ), whose seismic activity has continued since the Holocene period in the north, and the Kazankaya fault zones, which are thought to have been active since the Quaternary period in the south. These active faults found within the Amasya Shear Zone are also closely related to the North Anatolian Fault Zone (NAFZ). The Šapinuwa archaeological site was built on a unit composed of carbonate, claystone, sandstone and conglomerate from the Lower Middle Eocene (MTA, 2002). Archaeological excavations and archaeoseismological studies have revealed that very strong earthquakes in Šapinuwa during the Hittite period deformed the ground and caused significant damage to the structures (Süel & Süel, 2011; Drahor et al., 2023). An area of more than 100 hectares in the Tepelerarası locality of the Šapinuwa archaeological site was imaged by the magnetometer survey (Fig. 3a, Geoim Ltd., 2018). Thus, important data related to the urban distribution in this part of the city were obtained. First, it was revealed that the city has a settlement distribution that expands in approximately NE-SW and NW-SE directions. Due to the extensive fires in the city, it was observed that high magnetic values emerged, and they generally had a regular distribution. The same area contains other important building groups apart from the excavated structures (Buildings A, B, C, and D). It is thought that this confusion is caused by the deformations that occur in the structures because of large earthquakes, in the area that generally contains regular traces, but also shows a mixed magnetic distribution. Apart from the magnetometer survey, ERT, IPT, GPR, SRT, MASWT and self-potential methods have been used in the field. The GPR method did not achieve the desired success, especially due to the significant horizontal and vertical deformations occurred by earthquakes in the archaeological layers. Another result obtained from the field and showing the effect of the changes in the soil was obtained from the H area (shown by red rectangle in Fig. 3a). In the results of the magnetometer survey, the walls of the structures made of limestone are seen with distinct negative traces. On their interior, positive magnetic traces appear with a zigzag pattern. In the ERT depth slice (0.54–0.75 m), the wall made of limestone materials was revealed. However, a successful result could not be obtained in the corresponding GPR depth slices. During the excavation in this area, the structure given in the drone photograph (upper right corner of Fig. 3a) was unearthed at the first 70 cm depth. The structure here is very compatible with the model resulted from the ERT depth slice. It has also been observed that there is a significant agreement with the results of the magnetometer survey. An important earthquake trace was revealed during the excavations as they indicated that the burnt mudbricks of the limestone walls fell towards a distinct direction (from N to S). Additionally, since the environment was very mixed due to the earthquake, the stones and the unburned mudbricks of the wall were found in a very mixed condition. For this reason, positive magnetic traces appeared with a zigzag character. Due to the earthquake, a rise towards the surface was observed in the middle part of the area, while the presence of a collapse was observed at the other two edges. This case is clearly evident in the amplitudes of images obtained from the magnetometer and ERT surveys. This result is a unique example that demonstrates the success of the results of applied geophysical methods in determining the context affected by earthquakes in archaeological sites.

Fig. 3

(a) Results of the large-scale magnetometer survey, drone photograph of excavation, magnetometer image, GPR and ERT depth slices obtained from Šapinuwa archaeological site in Çorum. (Modified from Geoim Ltd., 2018). (b) Results of the magnetometer surveys and excavation photograph obtained from Hasankeyf archaeological site in Batman. (Modified from Geoim Ltd., 2013a)

5.2.2 Hasankeyf Archaeological Site

Hasankeyf and its surroundings, which have been an important settlement since the Neolithic period, were a trade and cultural centre in Mesopotamia. Within the scope of the Ilısu dam excavations, a geophysical study was conducted near the Zeynel Bey tomb related to the Akkoyunlu period (fourteenth century AD). The study area in the Tigris valley is located on a Quaternary alluvium found within the Şelmo formation from the Pliocene period on both sides of the river. This unit consists of gravel, sand, silt, and clay materials depending on the seasonal materials of the Tigris. The study area is located on the Southeast Anatolian Thrust Belt and in a region with high seismicity (Fig. 1c). During the geophysical investigation, magnetometer and GPR surveys were carried out (Geoim Ltd., 2013a). An image obtained from the magnetometer survey is given in Fig. 3b. Due to the previous restoration work conducted in the Zeynel Bey tomb and its surroundings, mixed magnetic traces have emerged in the image. However, traces of a structure with negative magnetic values are evident in the southern part of the area. This part, enclosed in the red frame of the image, can be seen in more detail on the right of the overall image. The excavation revealed the existence of a structure compatible with the results of the magnetometer survey. The materials found inside the building, which is made of limestone and buried very close to the surface, revealed that the building may belong to the Akkoyunlu period and may be related to a tomb. The structure was easily defined with sufficient magnetic contrast between the structure and the soil.

5.3 Grave Site

The study area, Ahlat Seljuk Cemetery, is located in the northwest of Lake Van in the Eastern Anatolia Region of Turkey, close to the active Süphan volcano, and it is covered with various lava and pyroclastic materials. Generally, andesite, rhyolite, basalt, cemented tuff, pumice stone and volcanic ash are observed in and around Ahlat. Additionally, the active Süphan fault is located close to the study area in the western part of Lake Van (Fig. 1c). The fact that the tomb stelae found in the study area generally collapsed in the E-W direction must be related to a great earthquake in the past. Ahlat, which was embraced by the Seljuks in 1070, became the capital of the principality established there. The cemeteries of this principality, which was one of the strongest among the first Seljuk principalities established in Eastern Anatolia, are also a unique characteristic. The study area, the Old Ahlat Cemetery, had an important place in the medieval Islamic world. There are 8169 tombstones of various types belonging to the Ahlatshahs, Ayyubids, Ilkhanids and Ottoman Periods between the twelfth and sixteenth centuries in the area. There are three types of burial structures in the cemetery. The first of these are the mausoleums, which are reminiscent of the Central Asian kurgans and are called “akıt” among the people. These tombs are called cellars in written sources. These underground structures are rectangular cellars made of cutting stones with volumes of 3.5–4 m³ or more (Fig. 4a, photographs from previous excavation). The top of these structures is made in the form of domes. Some of these structures, which look like a pile of earth from the exterior, have collapsed or have been dug to find treasure and their interiors have been explored. The second group is sarcophagus graves with triangular forms. The sarcophaguses are 250–300 cm long and 40–50 cm wide. The third type, located uppermost sarcophagus-shaped ones with a stele on the head, is the ones seen on the surface in the area. There are various motifs on the steles, and they are made of volcanic rock (ignimbrite) unique to Ahlat. These stelae of graves are 240–300 × 60–90 × 18–20 cm dimensions. A GPR study was conducted in order to reveal the shape, location, depth and dimensions of the unknown buried tombs in the area (Geoim Ltd., 2013b). The 40–60 cm depth slice, which shows several graves in the southern part of the cemetery, is given in Fig. 4b. Two different types of tombs can be distinguished in this figure. The first one is of the “akıt” type chamber tomb, and the shape and extension of this tomb are evident in the part indicated by the red ellipse. The tomb, which is approximately 10 × 10 m in size, has a general N-S and E-W directional extension. The volumetric view of this tomb is given in Fig. 4c. In the inner part of this tomb, which continues to a depth of about 80 cm, signal losses that can represent some entrances are seen, while the high amplitude reflection traces caused by some diagonal irregularities originating from the collapsed walls are also observed. To the southeast of this tomb, one side of another “akıt” type tomb is visible. Additionally, it is thought that there is another “akıt” type tomb in the part surrounded by the orange ellipse, but it may have been destroyed due to the weakness of the traces. The area surrounded by the blue ellipse is very complex. To the south of this, a part of another “akıt” type tomb extending in a slightly different direction is visible. In its northern part, the density of traces with negative amplitudes suggests that there are sarcophagus type graves buried in groups and that some of them may have been destroyed. However, since the traces are smooth, it can be thought that there may be another large “akıt” type tomb below them. Apart from these, those scattered throughout the area and extending in a certain direction should show sarcophagus graves, and those scattered in different directions should show the destroyed and buried stelae. The intense negative traces seen around positive traces were interpreted as a sign of destruction due to the excavation of the soil. The GPR study revealed that the “akıt” type tombs extend to a depth of 1 m from the surface, and that sarcophagi are buried close to the surface and their overturned stelae. Since the electrical contrasts were good between the structural elements made by volcanic materials used in the graves and soil, many burials were exposed. Additionally, the reason why the sarcophaguses are seen in different directions may also be from the presence of stelae that were destroyed by a possible earthquake and collapsed in different positions.

Fig. 4

(a) A photograph taken from previous excavations, (b) GPR depth slice and (c) volumetric GPR image obtained from Ahlat archaeological site in Bitlis. (Modified from Geoim Ltd., 2013b)

5.4 Preservation of Cultural Heritage and Restoration Studies

Integrated geophysical studies conducted in Agios Voukolos Church, an Orthodox religious building from the nineteenth century, located in the Basmane region of the city of İzmir (Figs. 1c and 5a), are representative of their innovations and integrated applications in interior spaces. The investigation had two purposes. The first was to reveal structural damage, such as cracks that could be found beneath the floor of the church, and possible crypt-type embedded features. The second goal was to determine the subsurface features in the backyard of the church, whether there was another structure beneath it. Magnetometer, GPR and ERT were used in the investigations. It is the first time that a magnetometer survey was applied indoors (Drahor, 2011b; Drahor et al., 2011). Figure 5b shows a grayscale image of the result of the magnetometer survey taken inside the church. Significant positive magnetic values are seen in the narthex and katholikon in the results of the magnetometer survey. The twin-positive magnetic traces that emerged in the middle of the katholikon are very similar in terms of size, shape, and amplitude. Among these, a negative trace emerges. The other trace, which has a rectangular shape, is seen to the south of the twin-positive traces. These traces extend in N-S direction and cover an area of 2 × 6 m. The forms and locations of the traces suggest that several crypts may have been hidden. This study shows that positive traces may be due to the presence of crypts, tombs, and other possible burials with high magnetic values. Negative traces may result from empty cavities. In the results obtained from a bidirectional GPR study from inside the church, high radar reflection traces were observed on the magnetic anomaly zones, especially in the locations of the twin anomalies. These traces generally reach a depth of 100–150 cm. The shapes of these traces reveal that possible buried structures are located under the floor of the church. Other high-amplitude signals occur mostly at the edges of the katholikon, and they correspond to both positive and negative regions in the results of the magnetometer survey. The volumetric image of the GPR results in Fig. 5c indicates a significant abnormal region at the location of the twin anomaly. This region corresponds to the centre and south of the magnetic twin traces. The volumetric image shows that the deeper parts of this structure can be more clearly defined. During GPR studies in the backyard of the church, two different antennas of 100 and 500 MHz were used. Two distinct horizontal reflectors emerged in the study, which was conducted using a 100 MHz antenna to reveal the subsurface features in the deep part of the ground where the church is located (Fig. 5d). The first reflector is a high amplitude near-horizontal layer and appears between 20 and 60 ns. The dashed lines drawn on this layer, where there are some divided and wavy zones in the reflection profile, reveal that this zone may have undergone deformation. Such a record should indicate separation and subsidence in the ground due to earthquakes or other structural features. The subsurface becomes much more complex after 60 ns. Obviously, the second reflective surface, which emerged between 60 and 140 ns in the middle of the measuring line, revealed that a structure from an older building phase could be found. Similar results were obtained from ERT studies (Drahor et al., 2011). The above clearly revealed the contribution of integrated geophysical studies to cultural heritage conservation and restoration studies. Additionally, the magnetometer survey, which was used for the first time in indoor studies, showed that the method could produce useful results if there are no significant magnetic trends from the interior of monuments.

Fig. 5

(a) Photograph, (b) results of the magnetometer survey, (c) volumetric GPR image and (d) reflection profile obtained from Agios Voukolos church in İzmir. (Modified from Drahor et al., 2011)

6 Conclusions and Discussions

This chapter presents a general review of archaeo-geophysical studies in Turkey. The effect of soil variability and climatic changes, tectonic effects and other similar geological changes crucially influence the success of geophysical studies in landscapes with characteristics similar to those of Anatolia. The above examples and case studies clearly demonstrate the need for detailed scientific research on these issues.

In the last decade, geophysical applications in the research of archaeological sites in Turkey have increased remarkably. This increase provides significant improvements in both the theoretical and field applications and has also an impact on the surrounding countries. The increase in the interest of the private sector in archaeological and cultural heritage investigations will also contribute to the improvement of the application methodologies and the development of new methods in the future. As Turkey is becoming one of the rising and industrialised countries of Europe and the Near East, this pace of development also poses a threat to Turkey’s archaeological and cultural heritage. Against this threat, the development of research focused on geophysics and other remote sensing applications will have a significant positive impact on Cultural Heritage Management. It is expected that further technological and methodological developments will emerge in archaeo-geophysical investigations, hopefully coupled with some legal regulations for their more systematic application in the management of archaeological sites in Turkey. Additionally, the increase in the interest of universities, private and public sectors on the topic will lead to sectoral growth and a further scientific development.