J. Appl. Geophs., Vol. 4, No. 1, September, 2005, - .

1

SHALLOW GEOPHYSICAL INVESTIGATIONS IN TABIT EL-

GEISH ARCHAEOLOGICAL SITE, SAQQARA AREA, GIZA GOVERNORATE, EGYPT

By Abd El-Gawad, A.M.S.*, Abd El-Aziz, M.A. ***, Abu El-Ata, A.S.A*,

Tealeb, A.A.** and Abd El-Aal, H.A.** * Geophysics Department, Faculty of Science, Ain Shams University, Cairo, Egypt.

** National Research Institute of Astronomy and Geophysics, Cairo, Egypt. *** Nuclear Atomic Corporation, Cairo, Egypt

ABSTRACT

Three shallow geophysical tools (microgravity, geoelectrical resistivity and seismic refraction) were measured to define the excavations probably occurred in the near-surface section of Tabit El-Geish sites, Saqqara area, Giza Governorate, Egypt. The topographical, geomorphological characteristics and the surface geological settings of the studied location were studied, in which the loose sediments of Quaternary age were cropped out on the ground of low surface features.

Microgravity survey in Tabit El-Geish site was executed utilizing the La-Coste and

Romberg gravimeters (models G-1024 and D-218). The acquired microgravity of the concerned area was reduced through the drift, terrain and latitude corrections. The resulted Bouguer gravity anomaly map of the studied site was modeled through Talwani and Ewing, 1960 and Plouff, 1976, and isolated into regionals and residuals through Geosoft package (1994) to check the locations of the possible cavities.

Geoelectric surveys in Tabit El-Geish site was conducted through the vertical

electrical soundings and horizontal electrical profiling using SAS 300c model terrameter. The produced geoelectrical data were interpreted qualitatively (through the iso-apparent electric resistivity contour maps and resistivity pseudo-sections) and quantitatively (through Zohdy, 1989 and Winsev 4.1, 1998) to delineate the locations of the caves.

Seismic refraction surveys in Tabit El-Geish were done using the model S2 echo-

Seismograph. The processing and interpretation of the gained seismic refraction data were carried out through Hagiwara’s method (1951), in which the travel time curves of the seismic profiles were established and the velocities and thicknesses of the layers were determined. The depth sections of the velocity layer structures were constructed through the ray-tracing approach to follow the holes configurations.

The integrated geophysical interpretations of the three utilized tools were evaluated in

the studied site in terms of archaeological assessment. They are succeeded in delineating ten excavations (seven large and three small) in Tabit El-Geish site. Further confirmative drilling programs are wanted for attesting the probability of finding these excavations and their interpreted locations and parameters.

A.M.S Abd El-Gawad et al.

INTRODUCTION

Geophysical methods have been used with increasing frequency in archaeology since 1946. Objects of archeological interest are usually located within a few meters of the surface. Therefore geophysical methods suitable for archeological exploration are those, which provide high resolution at shallow depths. In the present study microgravity, geoelectrical resistivity and shallow seismic refraction methods were used jointly in an attempt to scan the subsurface without destructing the soil. In this study, we had two targets, the first was to test each method over a known archaeological feature and the second target was to follow up the buried extension if that feature is existed.

The area under investigation, Tabit El-Geish site, Saqqara area, is located at about 20 km southwest of Giza town center. Saqqara area (Fig. 1) became the wonder of its age and an inspiration to later innovators, who perfected the pyramid to symbolize Egypt's civilization and commitment to eternal. This particular site was recommended to be surveyed by the chief inspector of Saqqara archaeological region, because he thinks in its promising for some tombs. There was an excavated hole in this site done by an Egyptian archaeological team in an attempt for exploring some tombs or any findings of archaeological interest.

Geomorphologically, Saqqara area can be divided into the following four major geomorphological units as shown in Fig. (2).

1) The flood plain and its fringes: The surface of this flood plain is gently slopes towards the north. The width of this flood

plain varies reaching its minimum in the south and maximum in the north. 2) The pediment plains: They are nearly flat erosional surfaces of low relief partly covered by alluvium that slopes away from the base of the mountain masses.

3) The Plateaux: They are extending in the N-S direction, the northern part of the plateau, which faces Abu-Sir village and called Abu-Sir plateau, the southern part over which the Saqqara pyramid and the various archaeological sites are found is called Saqqara plateau.

4) The foothills of the plateaux: These are located between the plateaux and the fringes of the flood plain.

The Study Area

Fig. (1) Location map for the area of study

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Geologically, the exposed rocks on the surface of the study area range in age from Late Cretaceous to Quaternary (Fig.3). The Eocene rocks (particularly the Saqqara Member) are exposed on most of Saqqara area. The Saqqara Member constitutes the bulk of Abu Sir and Saqqara plateaux. It consists of the following beds: 1) Basal shale of Saqqara Member: It is exposed at the foot of Abu Sir Plateau, and is composed of a marly shale bed. 2) Upper calcareous shale of Saqqara Member: It consists of alternating hard limestone and softer marls and shales.

MICROGRAVITY

PROSPECTING Microgravimetry is of increasing

interest to archaeologists in particular to search for ancient crypts or passages within the Egyptian Pyramids (Lakshmanan, 1991). The application of microgravity survey has been extended to the endoscopy of ancient monuments.

Blizkovsky (1979) provides an example of how a careful microgravity survey revealed the presence of a suspected crypt within the St. Venceslas Church, Toracv, Czechoslovakia, which was proven later by excavation work.

In the present work the gravity

survey was carried out using two types of high precision gravimeters (The La-Coste and Romberg. Gravimeters). The two

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Fig. (3) Surface geology map of Saqqara area and it’s surrounding

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Fig. (2) Geomorphological map of Saqqara area and it’s surrounding

(after Egyptian geological surveying authority, 1981)

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A.M.S Abd El-Gawad et al.

used gravimeters (Model G-1024 & Model D-218) are belongs to the National Research Institute of Astronomy and Geophysics. The model G-1024 meters have a worldwide range without resetting while the model D-218 meters have a range of 200 milliGals and a reset, which allows them to operate any place on the earth. The design of the gravimeters allows it to be very sensitive to small changes in the gravity field. The coordinates of the stations were determined by the system of GPS (Global Positioning System). The elevations of the gravity stations were measured with reference to the Geoids utilizing precise leveling. They were precisely measured using the Kern leveling instrument with an accuracy of 1mm. The topographic map of the Saqqara area includes the area under study is constructed and shown in Fig. (4).

Microgravity surveys were done for

the detection of cavities in the studied areas, which can be interpreted as archaeo-prospecting for the known and unknown tombs.

Tabit El-Geish area was surveyed by the gravity measurements where its area is of 40 meters length and 16 meters width, and of 1 meter spacing (Fig. 5). The gravity data resulted from the survey of the measured lines in the studied areas were reduced for the extraneous factors affecting the acquired data through the drift, terrain and latitude corrections, utilizing the modern techniques of gravity data reduction and processing.

The Bouguer gravity anomaly map

of Tabit El-Geish site (Fig. 6) is characterized by the presence of three incomplete gravity belts of varying polarities; central gravity high incomplete belt, northeastern gravity low incomplete belt and southwestern gravity very low incomplete belt. These gravity belts are trending nearly northwest southeast. It is clear that, the map is expressing the effects of the respective tombs. So, to investigate the possibility of any hidden cavity, it is necessary to calculate the gravity effect of the known tombs and cavities. In this study, the gravity effect of the modeled body on the considered profiles is calculated using the G-model software of La Coste and Romberg (1992) gravity meters version 2.2.

The Bouguer gravity anomaly maps of the studied area were subjected to

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Fig. (5) Gravity profiles layout at Tabit el-Geish site

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An excavated bore hole The study area

Fig. (4) Topographic map of Tabit el-Geish site (Saqqara)

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regional-residual separation using the frequency filtering of Geosoft package (1994). The residual gravity anomaly map (Fig. 7) represents the distribution of the gravity field after removing the regional effect. It reveals the local positive and negative gravity anomalies of very shallow nature. The residual anomaly map is characterized by the presence of three gravity belts of varying polarities; central gravity high belt, northern gravity low belt and southern gravity low belt. Every of these gravity belts is formed of a number of local gravity anomalies.

The resulted residual anomaly

maps of the studied site was modeled through the acquired gravity profiles to define the unknown near-surface features (excavations) of interest through the forward and inverse modeling processes introduced by Talwani and Ewing (1960) and modified by Plouff (1976) after carrying out the gravity body corrections of the known tombs and caves. The impact of microgravity method in archaeological prospecting involves the use of microgravity results in the archaeological prospecting of the considered area as means for defining the densities, extended depths of the excavations occurred beneath the measured gravity profiles in the near

surface section. One profiles is selected for presentation in this work at Tabit El-Geish site. This profile (VII) is traverse profiles trending often E-W. The illustration of each of these profiles involves: (a) gravity modeling process, and (b) comparable geologic section exhibiting the included cavities. The process of gravity modeling of profile IIV (Fig. 8A) reveals an eastward gravity high and westward gravity low. The comparable geologic section (Fig. 8B) reflects the presence of two caves, the western is of 4 m width, 2.3 m extent, 1.2 m depth and –0.58 g/c3 density contrast, while the eastern is of 3.4 m width, 2.6 extent .1.3 m depth and –0.43 g/c3 density contrast.

GEOELECTRICAL RESISTIVITY PROSPECTING

Geoelectrical Resistivity methods have been employed in archaeological investigations for many years. They were extensively used in Italy (Carabelli, 1967) and in England (Aitken, 1974; and Clark, 1986). Recently, they have been considered in archaeology as a mean for determining the depth and geometry of bodies in the vertical sections (Noel and Walker, 1990). For archaeological surveys, in order to produce useful

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Fig. (7) Residual gravity anomaly map of Tabit el-Geish site

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Fig. (6) Bouguer gravity map of the area under study

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A.M.S Abd El-Gawad et al.

electrical images of the ground, a computer-controlled electrical imaging system has been developed (Griffiths and Barker, 1993). The best-known method is the resistivity profiling, and typically Wenner or pole-pole array is used.

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Fig.( ) Gravity Modeling Along Profile "VI I-VII ' " at Tabit El-Geish site

A)Gravity modeling process

B)Comparable geologic section

FIG. ( 8 ) GRAVITY MODELING ALONG PROFILE VII- VII' AT TABIT EL-GEISH SITE

The geoelectrical surveys in the

regarded site and across the profiles previously identified were performed through the terrameter SAS 300C model. Both the Vertical Electrical Sounding (VES) survey using Schlumberger array as well as the Horizontal Electrical Profiling (HEP) using Wenner configuration were planned. Thirty-six VES (Fig. 9) and four HEP were measured through the Schlumberger array of electrode separation from AB\2 = 0.9m. to AB\2 = 30m. and Wenner array with electrode separation 1.5, 3, 5, 7 and 10 meters respectively.

The qualitative interpretation of

geoelectrical data obtained for the present work involves the preparation of the iso-apparent resistivity maps and pseudo-sections. The maps obtained by Wenner array were significant only for spacings of 1.5, 3 and 5 m, due to the limited size of the site and also the shortening of the profiles (about 40 m). Figure (10) shows the variations of the apparent resistivity at a spacing of 1.5m. The apparent resistivity reaches its maximum toward the northeast and also toward the south of the area (about 65 Ohms). Figure (11) exhibits the change of the apparent resistivity at a spacing of 3m, in which the values are varying from 3 to 15 Ohms. An interesting resistivity anomaly is located toward the southwest (about 15 Ohms). Figure (12) reveals the apparent resistivity of spacing 5m, in which the values vary between 1 and 4 Ohms. Also, there are two relative high anomalies, one to the northeast and the other to the southwest. It is clear the persistence of the southern anomaly in the three foregoing maps and the northeastern one in figures (10, 11 and 12).

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Fig. (9) Vertical electrical sounding location map.

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The iso-apparent resistivity maps

obtained by Schlumberger array are illustrated in figures (13,14,15,16,17 and 18). Figure (13) shows the iso-apparent resistivity map at AB/2 = 0.9 m, in which the values vary from 25 Ohms to 75 Ohms. These values are minimum toward the northern, northeastern and in the central parts of the area (about 35 Ohms), while these values are maximum toward the western and southwestern parts (about 70 Ohms) Figure (14) exhibits the iso-

apparent resistivity values at AB/2 = 2.1 m. It is apparently demonstrated that, the values are ranging between less than 5 Ohms toward the center of the map and more than 32 Ohms along the southeastern and southwestern part of the site.

The iso-apparent resistivity values at AB/2 = 3.8m. (Fig. 15) reveals that, the resistivity values reach their maximum toward the southwestern part of the area (about 32 Ohms) and the apparent resistivities attain their minimum toward the northern and central parts of the site (about 2 Ohms). The iso-apparent resistivity values at AB/2 = 7m (Fig. 16), reach their minimum (about 2 Ohms) toward the central, northwestern and southeastern parts of the map.

Figure (17) reflects similar pattern to figures (15 and 16), where the iso-

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Fig. (14) Iso-apparent resistivity map at AB/2 = 2.1 m.

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Fig. (13) Iso-apparent resistivity map at AB/2 = 0.9m.

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Fig. (12) iso-apparent resistivity map at a = 5 m. of the study area

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Fig. (11) Iso-apparent resistivity map at a = 3 m. of the study area

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Fig. (10) Iso-apparent resistivity map at a =1.5 m. of the study area

A.M.S Abd El-Gawad et al.

apparent resistivity is quite low toward the center of the map (about 3 Ohms) and high at its central west part (more than 41 Ohms). The iso-apparent resistivity values at AB/2 = 12m (Fig. 18) shows that, the values are minimum toward the center (about 3 Ohm) and maximum toward the northwestern and southeastern parts of the area (about 9 Ohms).

The thirty-six VES’s of the studied area are interpreted using Zohdy’s (1989) and Winsev 3.4 (1998). It is a forward and inverse modeling process for interpreting the resistivity sounding data in terms of a layered earth model, in which the results obtained showed that, geoelectrically the area could be divided into two layers. When plotting the values of the true resistivity of the first and second layers, two maps have been obtained. The values of the true resistivity of the first layer range between 20 and 75 Ohms (Fig. 19). The true resistivity of the second layer at Fig. (20) varies within a small range (from 1 to more than 12 Ohms) with a zone of relatively higher resistivity ranges from 7.5 Ohms to 11.5 Ohms, and extends from the northwestern, central and southern parts of the area.

It is noticed that, the high resistivity of the first layer corresponds to a small thickness value of 1 m, as shown in figure (21), which represents the thickness of the first layer in Tabit El-Geish. It is very interesting to observe that, the low resistivity values of the first layer correspond to high thicknesses reaching 5.5m. This might give us an indication about the existence of a saturated clay layer of high conductivity, which almost confirmed previously by the pseudo-sections.

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Fig. (18) iso-apparent resistivity map at AB/2 = 12 m.

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Fig. (17) Iso-apparent resistivity map at AB/2 = 9 m.

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Fig. (16) Iso-apparent resistivity map at AB/2 = 7 m.

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Fig. (15) Iso-apparent resistivity map at AB/2 = 3.8 m.

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SHALLOW SEISMIC

REFRACTION PROSPECTING The use of shallow seismic

refraction surveys for the detection of buried cavities is a new area of study and early results are encouraging (Al-Shayea, 1994, Gucunski et al., 1996 and Luke and Chase, 1997) to potential approaches for cavity detection. In the present work, using a 10 kg sledgehammer hitting a steel plate with a hammer geophone to

produce an impact, which provides the trigger impulse, generated the P-waves. This survey had been carried out along the profiles using a seismograph model S2 echo 24 channels, manufactured by Scintrix Company, Canada. To achieve the targets of the current work, the shallow seismic refraction surveys were carried out in Tabit El-Geish site were four longitudinal profiles 40 m the length of each profile (Fig. 5).

Data processing and interpretation were carried out using Hagiwara’s method. In this method, the velocity of each refractor and its thickness can be analyzed by using a set of reciprocal time curves. The depth and velocities of the different interfaces were calculated by using the previous algorithm, but with a software package (Seismic Refa RF”, 1996).

The velocity values of the first layer (Fig.22) vary from 250m/sec to 390 m/sec. These values form low velocity anomalies at the eastern parts, while the high anomalies locate the northwestern and southern parts. The low anomalies reveal mostly the places of tombs, while the high anomalies reflect the hard rock of the country rocks. The velocity values of the second layer (Fig.23) range from 350m/sec to 520m/sec. The low and high anomalies are located nearly at the same places of the first layer velocity map, indicating the locations of the tombs and the surrounding hard rocks. These hard rocks may represent the walls existed between the tombs or the un-drilled parts outlining the places of the caves. The depth values to the second layer (Fig.24) vary from 0.2m to 4m. The parts of considerable depths (1m to 3m) match

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Fig. (21) thickness of the first layer of the study area

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Fig. (20)|True resistivity map of the second layer

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Fig. (19) True resistivity map of the first layer

A.M.S Abd El-Gawad et al.

with the locations of tombs, while those of small depths (0.2m to 0.8m) coincide with the places of the surrounding walls or un-drillable section of hard nature.

It is worth-mentioning that, the

archaeological excavations concluded through the interpretation of the shallow seismic refraction surveys of the established site are those deduced through the seismic point of view. These excavations can be accepted or rejected partially or completely through the integrated evaluation of the three worked geophysical tools (microgravity, electrical

resistivity and shallow seismic refraction) explained later.

INTEGRATED GEOPHYSICAL-

ARCHAEOLOGICAL EVALUATION

The integration of these geophysical methods is essential for summing the sharing and varying characteristics in one and the same discipline, that wide spreading the domain of agreement between the deductions of these shallow geophysical tools. The minor differences arisen between these methods do not affect on the general agreement of the arrived conclusions, but they reflect self-enthusiastics in the field of archaeological application of the geophysical approaches. In this respect, the integration of three geophysical tools is better than two, and the integration of two geophysical tools is better than one for increasing the certainty required.

Moreover, the archaeological applications of the geophysical and geological interpretations mean the definition of the excavation of interest and determining its dimensions (width, extent, depth, density, resistivity, velocity… etc). To what extent this excavation is empty or filled with monuments and the types of these monuments, these are not the goals of the geophysical and geological applications, but these are the objects of the drilling as a discriminative archaeological approach. In other words, geophysics intends to locate cavities or excavations nevertheless these are tombs or secrete rooms or shallow tunnels, in which this is the role of archaeological drilling.

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Fig. (24) thickness of the first layer of the study area

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Fig. (23) velocity map of the second layer at Tabit el-Geish site

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Fig. (22) Velocity map of the first layer at Tabit el-Geish site

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In monitoring the integrated geophysical evaluation in terms of archaeological objects, the interpretation starts by the microgravity as a semi-detailed tool followed by the electrical resistivity followed by the seismic refraction as a detailed tool. In this regard, the excavations can be seen through the low resistivity, low gravity and low seismic depth. This is arisen by the fact that, the loose sediments filling these cavities are porous and saturated with water giving rise to lower physical properties, as compared to the neighboring walls and the surrounding country rocks, and as confirmed by the larger number of geophysical tools worked (three or two methods). The integrated geophysical interpretations are shown below:

1-Integrated geophysical interpretation of A-A/ section:

This is a longitudinal profile trending S-N. It is composed of three geophysical tools: Wenner resistivity, microgravity and seismic refraction (Fig.25). The Wenner resistivity (a) shows four high resistivity anomalies, three of them are small to the south, while the fourth is larger to the north, added to a low resistivity one to the south. These reflect a comparable shallow halo at the southern part of the inverse model resistivity section. The microgravity model (b) exhibits two anomalies, a major high superimposed by a small low to the north and a major low to the south. These confirm the existence of a large cavity to the south and a small one to the north. The seismic refraction depth section (c) illustrates a conspicuous low at the southern part. This attests the southern

cave deduced formerly. However, the integrated application of the three geophysical methods (a) expects the occurrence of a large excavation to the south and a smaller one to the north.

2-Integrated geophysical interpretation of B-B/ section:

This is a longitudinal profile orienting S-N. It consists of three geophysical tools: Wenner resistivity, microgravity and seismic refraction (Fig.26). In this respect, the inverse model resistivity section (a) shows four high resistivity anomalies (three smaller and one larger) and a low resistivity one located to the south. These reflect the existence of a cavity at the southern part of the section. The microgravity section (b) exhibits two highs (at the southern and central parts) and two lows (at the central and northern parts). These confirm the presence of two caves below the two low

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(c)Seismic Refraction Depth Section Along Profile"A-A/".

(d)Subsurface Setup, as concluded from integrated Interpretation.

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Fig. (25) integrated geophysical interpretation for profile a- a' at tacit el-Geish site

A.M.S Abd El-Gawad et al.

gravity anomalies at the central and northern parts. The seismic refraction depth section (c) illustrates two highs at the northern and southern parts and a low at the central part. These attest the occurrence of a major hole at the central part of the section. Accordingly, the integrated interpretation of the three geophysical methods (d) weights the fulfillment of three excavations, one to the south, one at the central part and one to the north.

3-Integrated geophysical interpretation of C-C/ section:

This is a longitudinal profile trending S-N. It is made up of three geophysical tools: Wenner resistivity, microgravity and seismic refraction (Fig.27) however, the inverse model resistivity section (a) shows a number of high resistivity anomalies and a low resistivity one occupied the southern part. These reflect the existence of a cavity at

the southern part of the section. The microgravity section (b) exhibits the presence of two lows at the northern and southern parts, with a high at the central part. This gravity high is implicated by a low of limited relief. These anomalies confirm the existence of three caves at the northern, central and southern parts of the section. The seismic refraction depth section (c) reveals three highs at the northern, central and southern parts, as well as two lows between them. These attest the occurrence of two holes at the northern and central parts. By this way, the integrated analysis of the three geophysical methods (d) expects the deduction of three excavations located at the northern, central and southern parts.

4-Integrated geophysical interpretation of D-D/ section:

This is a longitudinal profile orienting S-N. It is composed of three geophysical tools: Wenner resistivity, microgravity and seismic refraction (Fig.28). In this regard, the inverse model resistivity section (a) shows a lot of high resistivity anomalies and a low resistivity one lied at the northern part. These reflect the existence of a cavity at the northern part of the area. The microgravity section (b) exhibits two gravity lows at the northern and southern parts subtending between them a high at the central part. These confirm the presence of two caves at the northern and southern parts. The seismic refraction depth section (c) reveals four highs and three in-between lows. These attest the occurrence of three holes, one to the south and other two at the central part. Accordingly, the integrated geophysical interpretation of the three methods (d) weights the conclusion of four excavations, one to the

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(semifilled fragments filled cavity) (filled fragments filled cavity)

(d)Subsurface setup, as concluded from integrated interpretation

(c)Seismic refraction depth along profile"B-B/"

(b)Microgravity section along profile "B-B/"

(a)Wenner resistivity section along profile"B-B/ "

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(a)Wenner Resistivity Section Along Profile"B-B'"

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Fig. (26) Integrated geophysical interpretation for profile b- b' at

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north, one to the south, and other smaller two at the central part of this section.

The excavations of this site, as deduced from the integrated geophysical interpretations exhibited previously in Tabit El-Geish site, are scattered laterally according to a certain configuration (Fig.29). In this respect, the largest excavation (Ex. 1) occupies the northeastern part of the area in multi-rectangular shape, followed to the east by the second one (Ex. 2). The third excavation (Ex.3) is lied in the southeastern corner, while the fourth one (Ex.4) locates the central part. These are mostly the tombs of the senior persons lived at that time. Moreover, the excavations Nos. 5, 6 and 7, that occupy the southwestern part of the area are for the juniors. Added, the smaller cavities Nos. 8,9 and 10 were probably utilized as stores for the after death phase. The absence of the already existed tomb makes conspicuous difference in the distribution of these tombs.

CONCLUSIONS This work deals with the use of three

geophysical tools (microgravity, seismic refraction and resistivity) jointly to scan the shallow subsurface section, without destructing the soil or carrying out archaeological remote sensing in Tabit El-Geish site, Saqqara area, Giza

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Fig. (29) lateral excavation distribution at Tabit el-Geish site

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(a)Wenner Resistivity Section Along Profile"D-D/".

(b)Microgravity Section Along Profile"D-D/".

(c)Seismic Refraction Depth Section Along ProfileD-D/".

(d)Subsurface Setup, as concluded from integrated Interpretation.-8

-6

-4

-2

0

Sei

smic

Dep

th in

met

ers

-40

-30

-20

-10

0

10

observed gravitycalculated gravity

Gra

vity

in m

icro

Gal

s

RMS error = 13 microGals

-o.5

-0.95

Fig. (28) Integrated geophysical interpretation for profile D- D' at

Tabit el-Geish site

(a)Wenner Resistivity Sect ion Along Profle"C-C/ "

0 10 20 30 40

-1

-0.8

-0.6

-0.4

-0.2

Dept

h in

met

ers

(b)Microgravity Section Along Profile"C-C/".

(c)Seismic Refraction Depth Section Along ProfileC-C/".

(d)Subsurface Setup, as concluded from integrated Interpretation.-8

-6

-4

-2

0

Seism

ic D

epth

in m

eter

s

RMS = 13 microGals

-30

-20

-10

0

observed gravitycalculated gravityG

ravi

ty in

mic

roG

als

-0.84 -0.23-0.15

Fig. (27) Integrated geophysical interpretation for profile C- C' at

Tabit el-Geish site

A.M.S Abd El-Gawad et al.

Governorate, Egypt. The integrated interpretations were debouched in the archaeological assessment, area-wise, through the longitudinal and traverse profiles. The microgravity, the geoelectrical resistivity and shallow seismic refraction tools utilized in Tabit El-Geish site succeeded in detecting ten excavations: two biggest, five big and three small. Confirmative drilling program is advised for checking the occurrence of these excavations and their parameters, as well as for defining their monumental contents. This program should start from the well-known temples, to the less known tombs, to the unknown caves, cavities and holes.

REFERENCES

Aitken, M.J. (1974): Physics and archaeology. Oxford: Clarendon press, 286pp. Aitken, M.J.,G., and Rees, A. (1958). Magnetic prospecting: Antiquity 32, 270-271. Al-Chalabi, M. (1972): Interpretation of gravity anomalies by non-linear optimisation, Geophysical Prospecting, 20 (1) P.1-16. Al-Shayea, N.A. (1994): Detection of subsurface cavities using the spectral analysis of surface waves method, Ph. D. Thesis, University of Michigan. Blizkovsky, M. (1979): Processing and application of microgravity surveys. Geophysical Prospecting, 27 (4): P. 848-861. Conoco Coral and the Egyptian Petroleum Company, (1987): Geological map of Egypt, sheet No. 36 SW Beni Suef, scale 1-500000. D.H. Griffiths and R.D. Barker (1994): Electrical imaging in Archaeology, Journal of archaeological science No. 21, p.153-158.

El-Kady, G., (1995): Geophysical study for Saqqara area. M.Sc thesis, Mansoura University, Faculty of Science. Fahmy, T., (1998): Magnetic Prospection For Some Archaeological Sites in Egypt. Ph. D, Ain Shams University, Faculty of Science, Cairo, Egypt. Gucunski, N.Ganji, V. and Maher, M. (1996): SASW test in location of buried objects, proceedings, symposium on the application of Geophysics to Engineering and Environmental problems, compiled by R.S. Bell M.H. Cramer, Keystone, Colorado, 28 April-2 May 1996, P. 481-486. La-Coste & Romberg (1992): Instruction manual model G & D gravity meter: La-Coste&Romberg Inc., Austin, Texas. Lakshmanan, J. (1991): The generalized gravity anomaly; endoscopic microgravity. Geophysiscs, 56 (5): P.712-723. Luke, B.A, and Chase, D.S. (1997): Detecting caves using seismic surface waves, proceedings, Sixth Multidisciplinary Conference on Sinkholes and the Engineering and the Environmental Impacts of Karst, Sprigfield, Missouri, 6-9 April. Rotterdam: Balema, p. 419-424. Noel, M. and Walker, R. (1990): Development of an electrical resistivity tomography system for imaging electrical structures. In: Pernicka, E and Wagner, G.A. (eds), Archaeometry 90. Birkhauser, Basel, pp. 767-776. Plouff, D., (1976): Gravity and magnetic fields of polygonal prisms and application to magnetic terrain correction, Vol. 41, No.4, P. 727-741. Talwani, M. and Ewings, M., (1960): Rapid computation of gravitational attraction of three-dimensional bodies of

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arbitrary shape: Geophysics, Vol. 25, P. 203-255. Zohdy, A.R., (1989): A new method for the automatic interpretation of Schlumberger and Wenner Sounding curves, Geophysics, Vol.54, N.2, p.245-253.