Integrated Application of Geophysical Methods in Archaeology

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YARMOUK UNIVERSITY

FACULTY OF SCIENCE

Department of Earth and Environmental Sciences

Integrated application of geophysical methods for investigation of the

Al-Berktain archaeological site in the city of Jerash, Jordan

By

Ala'a Hussein Hawamdeh

Supervisor

Dr. Rasheed Jaradat

Co- advisor

Prof. Dr. Ziad Al Sa'ad

January, 2012


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DEDICATION

To my parents, for all their endless support,

Brothers,

Sisters, and

Friends


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ACKNOWLEDGMENTS

First and foremost, I would like to express my gratitude to my

advisor, Dr. Rasheed Jaradat. This thesis could not be written without his

guidance and support. And my thanks to Prof. Dr. Ziad Al Sa'ad for his

encouragement and support.

Special thanks for Mr. Abdullah Alawneh for his support.

Also I would like to express my gratitude to the Yarmouk University.


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Integrated application of geophysical methods for investigation of the

Al-Berktain archaeological site in the city of Jerash, Jordan

By

Ala'a Hussein Hawamdeh

Master of Science

Department of Earth and Environment Sciences

Yarmouk University, 2012

Advisor: Dr. Rasheed Jaradat

Co-advisor: Prof. Ziad Al Saad

Abstract

The joint application of Electrical Resistivity Tomography (ERT)

techniques involving the Wenner and Schlumberger electrode

configurations was conducted across four stations the ancient site of

Al-Berktain of Jerash, N-Jordan. It may be considered as the first

archaeogeophysical survey at this site. The objective of the work was

to determine the precise layout dimensions, and the depth of possible

buried structures within the site. The results showed high resistivity

anomalies located within the eastern, western and northern sides of the

pool. These anomalies were interpreted as a part of a general infra

structure of ancient man-made buried channels or supporting basins


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drainging out or feeding water to the two the water reservoirs

especially for the western and eastern side areas. Additionally, the

results indicated the presence of a very shallow compacted anomaly

that was interpreted as an ancient 0.5 meter pavement floor layer

extends over the northern side area. Within the pool floor the results of

survey showed anomalous thin shallow zone interpreted as a layer

limestone pavement of a thickness of 1 meter underlain by a thick

conductive sequence of wadi sediments and sediment fill material. In

order to obtain a more realistic image of the expected man-made

structures, 3D field surveying and inversion of measured data showed

the extension of some anomalies to the western side of the pool. It may

be concluded the site of Al-Berktain can be considered as part of the

general architectural context of the City of Jerash. Accordingly, other

uses for the two water pools can be implicated, rather than leisure,

such as water reservoirs to serve the city or irrigations purposes.

Key words: Electrical Resistivity Tomography, Geophysical, Wenner,

Schlumberger, Al-Berktain, Archaeological site, the two pools, Jerash.


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Chapter One

Introduction


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1.1 Introduction:Geophysical methods have been successfully applied to reveal and delineate

archaeological remains and have proved to be rapid, effective, and non-

invasive tools for the study of a broad range of various targets (Eppelbaum

et al., 2009).Geophysical surveys provide a ground plan of cultural remains,

and expose the probable layout, location, depth and physical properties of

archaeological settlements (Ekinci and Kaya, 2007).

Jerash (Gerasa) is one of the major cities in northern part of Jordan that

historically belonged to the Decapolis (Aubin, 1997). Much of the

archaeological value of Gerasa is mainly contained within the premises of

the surrounding walls of the ancient city.

In this study an attempt will be made to explore this archaeological site

using an integrated geophysical techniques approach. Specific survey

objectives often cannot be met by applying only one geophysical technique.

Al-Berktain site represented a place of sanctuary for the inhabitants of the

ancient city of Gerasa (Segal, 1994). Recent archaeological excavations

within Al-Berktain revealed a number of structures, such as: a roman

theatre, a mosaic floors and a roman bath (Malkawi, 2006). Figure 1.1.


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Figure 1.1: A closer look to the survey area. The imposing ruins of the

pool, theatre, and a roman baths are shown in the aerial photo.

There are ambiguities and limitations restricting the use of methods in

different cases, for instance, in resistivity surveys thin beds and smaller

features may not contribute their signature to an apparent resistivity curve or

a resistivity image, unless they create especial high resistivity contrast with

surrounding geology. Noise is another problem that all geophysical data

contain to some degree, and can mask desired geophysical signals. For these

reasons, Wenner resistivity tomography and Schlumberger resistivity

tomography methods were used together to provide important cross-checks

for interpretations (Burger et al., 2006). The ability of detecting the man-

made structures, and the low cost of the investigation and the fact that there

is resistivity contrast between these structures and the surrounding soil, all


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made the resistivity method one of the most commonly applied techniques

for geophysical investigation in archaeological sites (Ekinci and Kaya,

2007). By the conventional resistivity mapping surveys, a map is generally

produced using the apparent resistivity data which is a function of the

subsurface resistivity distribution and of the geometry of the electrodes.

Tomographic resistivity data are collected a long a measuring line by

sequence of a selected configuration for building up a pseudosection (2D) or

obtained from a selected area by different arrangement of electrode

configurations for 3D surveys (Drahor et al., 2008). Compared with

conventional electrical soundings and profiling, the electrical profiling is the

most common method. It yields more detailed structural information (Storz

et al., 2000).

1.2 Significance and Objectives of the Study:

Gerasa (Jerash) is one of the main archeological cities of the Middle East

region that is still underexplored. The site of Al-Berktain (the two pools) is

located outside the ancient walls of the city. It is hoped that this study will

be able to explore possible subsurface structures adjacent to the pool body,

draw the attention to the archaeological value of the site, open the


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opportunities for future investigations, and provide the means for necessary

site preservation.

The main objectives of this study are to:

Locate potential subsurface structures and their extensions

using integrated application of Electrical Resistivity

Tomography (ERT) techniques.

Determine the precise layout, dimensions, and the depth of

possible buried structures within the study area.

Set priorities and provide recommendations for future

excavation projects within the proposed archaeological site.

1.3 Literature Review:

Previous literature related to the site of Al-Berktain is very limited. Most

of the available data is mainly in the form of unpublished reports of

previous excavation campaigns. Al Momani et al. (2002) conducted

archaeological excavation works in Al-Berktain historical site (Jerash), and

provided logging for the previous excavation projects which discovered a

Roman bath and exhibited a number of covered features within the site.

Balawneh and Malkawi (2005) reported the results of the 2002 campagin

project of the archeological survey to excavate roman archeological ruins


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southern theatre in Al-Berktain site. A number of buried chambers and

relicts were reported.

Malkawi (2006) reported the results of archaeological prospecting study at

Al-Berktain site in Jerash. Significant findings indicated the presence of

many Roman ruins at the site.

The application of geophysics in the field of archaeology in Jordan is

growing more and more and it has proved to be very effective in delineating

potential sites of investigation. For example, Qazaq (1995) exerted

magnetic geophysical survey at Yasileh Archeological site, Northern

Jordan. His results indicated that magnetic surveying succeeded in locating

archeological features that have not been discovered by excavation, and it

had proved to be successful for the first time in Jordan to locate buried

archeological features in the Yasileh site. Two rectangular buried features

were detected in two areas, area and area , with probable dimensions of

35 x 40m and 25 x 35m for area and area , respectively.

Witten et al. (2000) utilized a range of geophysical surveys;

Electromagnetic Induction (EMI); Ground-Penetrating Radar (GPR); and

Magnetometry, in the Jebel Hamrat Fidan, south Jordan. They aimed to help

locating buried remains of architectural and industrial features from early

mining and metallurgical operations; including copper ore bodies or voids.

Magnetometry and ground penetrating radar provided little useful

information. Buried stone walls were apparently masked by numerous


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magnetic stones on the ground surface making magnetometry useless.

Reflections from known strata demonstrated that radar penetrated the

ground adequately; known shallow buried walls were not recognizable.

Electromagnetic induction produced maps of linear and rectilinear features

that suggested spatial distribution of widespread buried stone walls suitable

for future excavation.

Batayneh et al. (2001) conducted a magnetic and resistivity geophysical

surveys over the Tell al Kharrar archaeological site, at Wadi al Kharrar, east

of Jordan River, Jordan, to map buried structures, identify target zones

quickly, thereby reducing the required amount of costly excavations.

Measurements of the total magnetic field and pole-dipole resistivity surveys

yielded anomalies, which are associated with walls, floors, mosaic floors

with ornaments, iron construction tools, channels, and a church abattoir.

Conyers et al. (2002a and b) used GPR maps and images as a guide to

excavation strategies at Petra site in, Jordan. A number of buried buildings

were discovered, as well as stratigraphic horizons that were later found to

contain evidence of ancient gardens. The GPR profiles and amplitude slice-

maps and renderings were an excellent tool for mapping both subsurface

features and stratigraphic interfaces of interest.

Oleson et al. (2002, 2003, and 2004) carried out geophysical surveys

(electrical resistivity, magnetic gradiometry, and ground-penetrating radar)

at Humayma site (southern Jordan). GPR was the best tool for locating


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buried structures, but only if the profile spacing was small (around 1m).

The magnetic gradiometer generally was only able to detect fairly shallow

targets (upper meter). The data collected with the capacitively-coupled

resistivity meter was useful for identifying deeper targets (>1m), but did not

have the vertical or horizontal resolution potential of the GPR. GPR and

magnetic geophysical surveying successfully indicated the presence of

buried structures at the site. They made an extensive survey, and detected

several archeological remains based on those geophysical surveys which

proved very effective in revealing the plans of structures known but not yet

excavated.

Batayneh et al. (2007) applied a suite of geophysical methods of

microgravity, magnetometry, and electrical resistivity tomography (ERT)

methods to investigate sites within Umm er-Rasas archaeological site,

Madaba. Geophysical methods aimed at obtaining information about the

subsurface and associated buried structures beneath the Late Byzantine

Lion Church, in the ancient town of Umm er-Rasas (Kastrom Mefa'a).

Microgravity and magnetometry methods found a number of structures with

contrasting physical properties to those of the surrounding material. The

archaeological interpretation of such structures is in terms of two possible

floors of a building with remains of walls, rooms, paths and foundations.

Resisitivity data showed a highly conductive region close to the church

wall.


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Baker and Ambrose (2007) examined the application of geophysical

surveys that were conducted on and around the site of a 4th Century Roman

fort in Southern Jordan from 2002-2005 as apart of the Humayma

Excavation Project. Data were collected in a series of 1-m-spaced profiles

within the 150m by 200m Fort and collated to generate 3D volumes. Data

yielded good details of interior structures (walls and potential tiled floors)

and exterior features (defensive ditches, claviculae, the Via Nova).

Batayneh (2010) exploited magnetometry and pole-dipole electrical

resistivity geophysical methods for assessing their capability in the

detection of Nabataean Hawar (Humayma) archeological site in the SW-

Jordan. A number of magnetic stations and two pole-dipole resistivity

traverses were carried out in the investigated area. Magnetic method found

structure with contrasting physical properties to those of the surrounding

material. The archeological interpretation of such structure is in terms of

rectangular cistern (pool) with dimensions 2616 m. A probable location of

two buried walls spaced 16 m are indicated by low resistivity values.

In a regional example, Weinstein-Evron et al. (2003) Conducted

geophysical investigations in el-wad cave, Mount Carmel, Palestine.

Ground Penetrating Radar (GPR) and Seismic refraction provided similar

results. A Continuous Vertical Electrical Sounding (CVES) geoelectric

survey in the (collapsed) Misliya Cave indicates a low resistivity layer


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suggesting that lithified archeological deposits, of ca. 4 m, are preserved at

the site. At the bottom of the cliff and across the hypothesized cave (or

chamber), the used two-layer model showed a low resistivity (100200

ohm-m) layer, overlying a layer of high resistivity (800010,000 ohm-m).

Yaliner et al. (2008) reported the results of a temple discovery at the

archeological site of Nysa western Turkey by applying GPR method. They

described the discovery of a new temple in the ancient city of Nysa (western

Turkey). Testing two different frequency of GPR antenna showed that the

roots of olive trees hide the buried archaeological remnants if a 500 MHz

central frequency antenna is used. This difficulty was overcome by using

the 250 MHz GPR antenna. Therefore, this suggested that relatively lower

frequency antennas should be used in areas covered by trees. In order to

map the 3D distribution of the archaeological remnants and determine their

size they had carried out their surveys in a grid manner. This allowed them

to reveal the architecture of the temple in fine detail, which, in turn, allowed

the archaeologists to expedite their archaeological excavation.

Boyce et al. (2009) employed magnetic detection of ship ballast deposits

and anchorage sites in King Herod's Roman harbour, Caesarea Maritima,

Israel. Their geophysical investigations at Caesarea Maritima in Israel had

discovered a thick, laterally extensive ballast layer in the area seaward of

the 1st c. BC Roman harbor, large quantities of Late Roman and Byzantine

pottery, local sedimentary boulders (kurkar sandstone, limestone cobbles)


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and foreign igneous and metamorphic boulders (granite, schist, volcanics;

ca. 50%). Magnetic surveys at Caesarea have identified several magnetic

anomalies in the area seaward of the main harbour that mark the location of

ballast deposits and ship anchorage areas.

1.4 Structure of study:

This thesis is divided into five chapters following the introduction in

chapter one, a general view about the study area, topography, geological

setting and local/regional geological structures are described in chapter two.

A description of the methodology and field techniques used in this thesis is

given in chapter three. Results and analysis of geophysical data are

presented in chapter four. Finally, the last chapter provides the conclusions

and some recommendations.


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Chapter Two

History, geography

and geological

settings of the study

area


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2.1 Archaeological backgrounds:

The ancient city of Jerash (Gerasa) is one of ten Greco-Roman cities which

formed the Decapolis (figure 2.1), that took its name from the confederation

of the ten cities that domainted its extent. During the first and second

century AD all the cities of the Decapolis developed into grand

metropolises decorated with many fine civic and religious building

(Browning, 1982).


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Figure 2.1: The region of the Decapolis (Atlas Travel and Tourist Agency,2007).

The landscape of Jerash represents an evolution of human society because

of its various architectural monuments and settlements that refer to many

periods like, Prehistoric, Roman and Islamic periods. The succession of the

ancient cultures in Jerash gave the ancient city its historical value.

Excavations have exposed architectural remains and artifacts from

settlements that existed on the south part of the site, around the zeus Temple

and Camp Hill, during the middle and late Bronze Age (1600-1200 BC)

(Khouri,1988 & Zayadine, 1988) and the Early Iron Age (1200-900BC)

(Kouri, 1988 & Borgia, 2001).


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The site appears to have been abandoned from the 8th

to 3rd

Centuries BC

before the advent of Hellenism, there was a settlement at the site known by

its indigenous Arab/Semitic population as Garashu. The name was later

Hellenized into the Roman name Gerasa, which was finally arabised to give

us the modern name of Jerash. Recently the excavations have proved

liberary references from the Classical period which indicate that the first

major urban settlement at Jerash was established in the Hellenistic period,

sometime after the armies of Alexander the Great conquered the region in

332 BC. Architectural remains confirm that a Hellenistic settlement

certainly existed at Jerash by the 2nd

Century BC, when the region was part

of the Seleucid Empire (Khouri, 1988).

The city and other Decapolis cities were conquered by Pompey in 63 BC,

which ended up being a positive development (Kraeling, 1938). The

dramatic events associated with the Jewish revolt in 66AD and the

consequent representation by Vespasian and Titus do not seem to have

affected the city's gradual process of urban development (Borgia, 2001).

Jerash lost its autonomy under Emperor Trajan, buthis annexation of Petra in

106 AD brought the city even more wealth. Parapetti mentioned that there

are two well known inscriptions on a panel of the North Gate which proved

the reality of the political and commercial situation in Gerasa. The city plan

with its colonnades flanking the main streets where they were commonly

adopted after the beginning of the 2nd

century AD (Khouri, 1995). In 129


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AD, the monunental triumphal arch at the southern end of the city was

erected to celebrate the visit of emperor Hadrian; this was the golden age of

Jerash (Harding, 1973). During the 2

nd

century, several temples were built

including the Temple of Artemis (in 150 AD) and Temple of Zeus (in 162

AD). After 330AD, the emperor Costantine declared Christianity as the

official religion of the Eastern Roman. Under Justinian, 531-565 AD, there

was a rise in prosperity, and more than seven churches have been built in

this period. Inscriptions record the erection of other public buildings

(Harding, 1973). The city was invaded by the Persians in 614 AD, captured

by Muslims in 635 and badly damaged by several earthquakes in the 8th

century (Alanen, 1995). In 749AD a great earthquake struck the city

(Khouri, 1988).

The investigated area is located due north of the north gate of Jerash. Its a

large pool that is called locally as the Berktain or Al-Berktain; the two

cisterns. In fact, it is one large pool body devided into two basins that is

generally rectangular. The structure is 45.88 m wide and 89.55 m long,

oriented due north and south. At 18 m from the southern end of the structure

a heavy wall (2.7 m thick and lower than the western edge of the pool)

divids it into two unequal parts may be to situate opposite to the western

theatre that rest about 8m upon the slope of a western hill, or to regulate the

depth of water in the upper, or main pool.


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The pool was built in the early 3rd

century, and the theater somewhat later.

A sixth-century inscription says that the notorious Maiumas water festival

was held at Al-Berktain, a festival frowned on by the Christian element, as

it involved, among other things, mixed bathing (Kraeling, 1938). When

Burckhardt visited the site in 1812 he described it as a "most romantic

spot," where "large oak and walnut trees overshadow the stream." (Segal,

1995).

Figure 2.2: The site of Al-Berktain.


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The restoration and excavation projects at Al-Berktain are very few. The

recent works were achieved and exposed a number of remnant roman ruins;

e.g. the roman bath (Figure, 2.3). Restoration project for the site was carried

out by the Royal Corps of Engineers of the Jordanian Armed Forces during

the sixties of the last century. No documentation was found for their

activities. Locals from the regions indicated that most of the work was

related to reconstructing the two pools and clearing off their basins and their

surrounding basins. Heavy machinery was used for that purpose.

Figure 2.3: Excavation works during 2002 at the site of Al-Berktain by

support of the Jordanian department of the Antiquities (DoA).


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2.2 Location of the study area:

The study area locates 1,200 meters from the north Gate of the roman city

of Jerash, N Jordan. It is delimited between 772300 E, 3575300 N assuming

the UTM, Zone 36 coordinate system (Fig. 2.4).

The study area resides within the alluvial plain of Wadi El Dair Valley

(Fig. 2.5), that is a north-south draining stream valley that is used to feed

the northeast parts of the old city with fresh water. The valley floor is

covered by soil deposits, with relatively low slopes. To the east, the valley

is wider. The altitude of the area is between 625 m A.S.L, in its

southeastern part, and 633 m A.S.L in its northwestern part.

It receives a relatively high mean annual rainfall 500mm/yr. summers are

fairly hot, with a mean monthly and yearly temperature of 20o

c for the

months July, August and September and with an absolute maximum of

35oc.Winters are cold with a mean daily temperature of less than 10

oc.


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Figure 2.4: Jordan map showing the location of the study area. The right

image, facing north, shows the survey area. It is marked with a red

rectangle.


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Figure 2.5: Topographic map showing the location of the study area next to

Wadi El Dair valley (Modified after the 1:50:000 sheet of Jerash produced

by the Royal Geographic Center).


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2.3Geological Setting:

The geology of the study area is characterized by Quaternary sediments

that are represented by thick brown to red soil deposits. Figure 2.6

illustrates the different formations outcropping within the study area and

the vicinity. The outcropping rocks predominately consist of limestone

(Burdon, 1959). Rimawi (1985) provided a summary for the dominant

sedimentary rocks outcropping within north Jordan. Within the study area

Ajlun group is dominated by the Naur Formation of the Cenomanian age.

2.3.1 Ajlun Group (Cenomanian to Turonian):

Ajlun group is overlain unconformably by chalk, limestone, marine sediment

and dolostone with a maximum thickness are in the north, forming extensive

outcrops from Ajlun to Amman, while to the south thickness decrease

(Burdon 1959; Masri 1963). In the Cenomanian, a major marine

transgression, which had reached west Jordan, Lebanon, and Syria in the

lower Cretaceous, reached the northern part of east Jordan and spread

southwards. During the Turonian, the seas spread farther south, and marine

beds, mainly limestones and dolomites with some marls, were deposited. All

these beds have been grouped into the Ajlun series, named from the major

outcrops around Ajlun. At the beginning of the Senonian (Conacian-

Santonian), the types of rock deposited in this transgressive sea changed;

limestones and dolomites were replaced by chalks, flint and marls which

were sometimes bituminous. Within the study area this group is dominated


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by the Naur Formation of the Cenomanian age. Naur limestone belogs to

Ajlun series occupying most of the country between Irbid and Amman.

(Burdon,1959).

2.3.2Naur Formation(Cenomanian):

The majority of the formation is poorly exposed, and in many areas it is

covered with soil or calcrete as well as vegetation. The formation

predominately consist of limestone; grey to yellow-grey, frequently nodular

and marly, fossiliferous, medium to thick bedded, locally massive, spary

micrite, to micrite alternating with yellow to white grey marl enclosing

medium to thin beds of nodular and fossiliferous limestone, and with lenses

and thin beds of green grey calcareous mudstone and gypsiferous clay

(Wetzal and Morton 1959; Basha 1978; Dilley 1985).


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Figure 2.6: Simplified geological map of Jerash, showing the major

outcropping geological formation in the area of study (Abu-Jaber et al.,

2009).


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Table1: Presents the geological description of the dominant rock units of

N. Jordan, (Modified after Rimawi (1985).

E

poch

Age Group Formation Rock type Thickness(m)

UpperCretaceous

Maestrichtain

BalqaMuwaqqar

Chalk, Marl and Chalky Limestone.

60-70

Campanian Amman

Chert, Limestone with phosphate.

80-120

Santonian Ghudran

Chalk, Marl and Marly Limestone.

15-20

Turonian

Ajlun

Wadi As Sir

Hard Crystalline Limestone.Dolomitic and some Chert.

90-110

Cenomanian

Shueib

Hight Grey Limestone interbeded withMarl and Marly Limestone.

75-100

Hummar

Hard dense Limestone and DolomiticLimestone.

40-60

Fuheis

Gray and Olive Green soft Marl.Marly Limestone and Limestone.

60-80

Na'ur

Limestone interbeded with a thicksequence of Marl and MarlyLimestone. 150-220

Lower

Cre

taceous

Albian-Aptian Kurnub

Mssive White and VaricoloredSandstone with layers of Reddish Siltand Shale.

300


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Chapter three

Methodology


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3.1 Preface:

This chapter describes the methods used in this study that depend on the

application of electrical resistivity geophysical methods to explore potential

subsurface structures within Al-Beriktain archeological site. The flowchart

showing the different stages of works is given in Figure (3.1).

Figure 3.1: Schematic flowchart illustrating the general procedures of the

methodology of this study.


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3.2 ElectricResistivity Survey:

3.2.1 Introduction:

Electrical measurements are the most commonly used method to

investigate subsurface conditions in an area. The electrical current is driven

through the ground and the resulting potential differences are measured at

the surface. Anomalous conditions within the ground, such as poorer

conducting layers, are inferred due to the fact that they deflect the current

and distort the normal potentials. The technique of resistivity surveying was

developed by Conrad Schlumberger, who conducted the first experiments

(1912) in the fields of Normandy (Sharma, 1997).

The resistance of a block of material can be calculated by measuring the

voltage drop (V) a cross the block and the intensity of a passing current (I)

through the block using Ohms law:

R=V/I . eq. 1

The resistivity of a block of material () can be calculated in (ohm.m) by

combining the electrical resistance(R) produced by the entire block, the

length of the block (L), and the area (A) using equation 2:

= R (A/L) .. eq. 2


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Many materials can have the same resistivity that makes the resistivity

information insufficient to identify the material (Christensen, 2000). Even

after the resistivity distribution is determined, it is not possible to fit this

distribution into a subsurface geology model without having at least a

general idea about the local geology, since the resistivity of geological

materials exhibit one of the largest ranges in all physical properties. Large

differences in resistivities are clear between unweathered and weathered

rocks and also between water and frozen ground that prove the effect of the

age of a rock (Reynolds, 2005). Resistivity ranges of some common

geologic materials are presented in Figure (3.2),

Figure 3.2: Typical ranges of resistivities of earth materials (adopted from

Palacky, 1987).


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Electrical resistivity surveying can be simply implemented using a circuit

composed of an electrical current source, four electrodes and appropriate

current and voltage measuring devices. The system introduces an electric

current of a specific value ( ) through two current electrodes (C1 and C2)

and then the device measures the voltage (V) between two potential

electrodes (P1 and P2), as shown in Figure 3.3. Potential at each electrode is

determined due to the current sources using these equations:

VP1 = ( I \2 r1- I \2r2). (eq.3)

VP2 = (I \2 r3- I \2r4) ...(eq.4)

where is the resistivity, I is current intensity, and r is electrode

separations.

The potential difference V= VP1 VP2 is estimated by:

V= I \2 (1\r1 -1\r2 -1\r3 +1\r4)(eq.5)

The above equation can then be solved for the resistivity (. In a non-

homogeneous earth the resistivity which is measured is not actually the true

resistivity of the subsurface. For an earth with more than one layer, the

apparent resistivity ( measured will be an average of the resistivities of

the additional layers. The apparent resistivity data needs to be interpreted in


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terms of a subsurface model in order to determine the true resistivities of the

layers (Reynolds, 1998).

Figure 3.3: Electrical resistivity electrode field setup.

3.2.2 Electrical Resistivity Tomography (ERT):

Electrical Resistivity Tomography (ERT) is a technique used to image

vertical and horizontal subsurface variation in resistivity. This can be

achieved by collecting large number of samples along a profile using a

given electrode interval. In order to sample a deep depth of penetration the

electrode interval is extended further (Figure 3.4).

Advanced multi-electrode resistivity meter systems, allows fast imaging of

vertical and horizontal variations of resistivity. It is easier using todays

instruments to acquire huge number of data points comprising 2D cross-


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sections or profiles or a 3D data cube of resistivity data of the subsurface.

On the basis of the distribution of resistivity within measured profiles, an

accurate interpretation of the subsurface geologic setting can be made.

Figure (3.5) shows the arrangement of electrodes for 3D surveys.

Figure 3.4: ERT imaging sequence setup (adopted from Loke, 1994).


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Figure 3.5: The arrangement of electrodes for 3-D survey (adopted from

Loke, 1994).

Different electrode configurations can be employed, which tend to vary in

their vertical and horizontal resolution limits, such as (Figure 3.6):

1- Wenner electrode configuration:

Assumes a constant equal electrode separation, where C1-P1, P1-P2, and

P2-C2 separations are kept fixed (a). Apparent resistivity can be

estimated as:

i

Va

a

2 ... (eq.6)

2- Schlumberger /gradient electrode configuration:

Assumes variable electrode separation where the separation between P1-

P2 is much less than C1-C2, such that C1-C2 is less than or equal to

5(P1-P2) interval. Apparent resistivity can be estimated for the Gradient

configuration as:

i

V

xL

xL

la

22

222

2

... (eq.7)

Whereas for the Schlumberger configuration the equation can be written as:

i

V

L

l

l

La

2

22

1

2

... (eq.8)

3- Dipole-Dipole electrode configuration:

Assumes a fixed distance between C1-C2, and P1-P2 of (a), such that

C2-P1 is multiple of current or potential separations (na). Apparent

resistivity can be estimated as:


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i

Vnnan

a

21 ... (eq.9)

4- Pole-Dipole electrode configuration:

Assumes a fixed distance between P1-P2 of (a), such that C1-P1 is

multiple of current or potential separations (na), and that C2 is kept at a

distant location perpendicular to profile trend. Apparent resistivity can

be estimated as follows:

i

Vnan

a

12 ... (eq.10)

Figure 3.6: Different electrode configurations of ERT (Reynolds, 1998).


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For the purpose of this study, the electrode configurations of Wenner and

Schlumberger were adopted. The following subsections shed the light on

the characteristics of these types.

3.2.3 Wenner array

The Wenner array is a suitable array for the solving of vertical changes (i.e.

horizontal structures). Compared with the other arrays, the Wenner has a

moderate depth of investigation (Loke, 1999). For this array, the geometric

factor is 2a, which is smaller than the geometric factor for other arrays.

Among the common arrays, it has the strongest signal strength. It has the

highest signal-to-noise ratio. One disadvantage of Wenner for 2D survey is

the relatively poor horizontal coverage as the electrode spacing is increased.

This could be a problem if you use a system with a relatively small number

of electrodes. The Wenner array has three different variations fig. (3.7). The

normal Wenner array is actually the Wenner alpha array. The median depth

of investigation for Wenner array is approximately 0.5 times the spacing

used (Milsom, 2003).


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Figure 3.7: The different variations of Wenner array. C1, C2 and P1, P2

denote the positions of the current and potential electrodes (adopted from

Loke,1999).

3.2.4 Schlumberger array

Schlumberger array represents a new hybrid between the Wenner and

Schlumberger arrays arising out of relatively recent work with electrical

imaging surveys. This array is moderatly sensitive to both horizontal and

vertical structures. The median depth of investigation for this array is about

10% larger than that for the Wenner array for the same distance between the

outer (C1 and C2) electrodes, but the signal strength for this array is smaller

than that for the Wenner array.


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The Schlumberger array has a slightly better horizontal coverage compared

with the Wenner array. For Wenner array each deeper data level has 3 data

points less than the previous data level, while for the Schlumberger array

there is a loss of 2 data points with each deeper data level (Reynolds, 1998).

The horizontal data coverage is slightly wider than the Wenner array.fig.

(3.8).

Figure 3.8: Schlumberger array.C1, C2 and P1, P2 denote the positions of

the current and potential electrodes (adopted from Loke, 1999).

3.2.5 Resistivity Inversion Modelling of ERT:

Inversion in geophysics basically is the back calculation of subsurface

parameters by iteration of a computer generated ground model until the

model-predicted measurements fit the field measurements (pseudosection).

Figure (3.9) illustrates a general workflow for the inversion modeling

procedure.


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Figure 3.9: The resistivity inversion procedure (Basokur, 2004).

After the data from the field were collected, gathered resistivity profiles

were modeled and interpreted using the inversion modeling RES2DINV

software. For the purpose of this study collected geoelectric data have been

processed by using the RES2DINV and RES3DINV (V. 3.55) inversion

modeling softwares (Loke, 2004).

These softwares are numerical inversion softwares that produce 2D or 3D

resistivity models of the subsurface using data extracted from electrical

resistivity tomography method (Griffiths and Barker, 1993). The true

subsurface resistivity model of the subsurface is estimated by inversion of

the measured apparent resistivity adopting 2D or 3D geoelectric data

inversion routines. The inversion routines are based on an iterative error

minimizing smoothness-constrained least squares method (deGroot-Hedlin

and Constable 1990; Constable et al. 1987; Sasaki 1989, 1992; Loke and


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Barker 1996; Loke and Barker, 1996a; Loke and Barker 1996b; Tsourlos

1995). Figure (3.10) shows a general flowchart for the resistivity modeling

process.

Figure 3.10: Resistivity modeling process using RES2DINV software

(adopted from Loke, 2004).

The 2-D model used by this program divides the subsurface into a number

of rectangular blocks. The purpose of this program is to determine the

resistivity of the rectangular blocks that will produce an apparent resistivity

pseudo section that agrees with the actual measurements. The used

optimization method tries to reduce the difference between the calculated

and measured apparent resistivity values by adjusting the resistivity of the

model blocks. A measure of this difference is given by the root-mean-

squared (RMS) error. However the model with the lowest possible RMS

error can sometimes show large and unrealistic variations in the model

resistivity values and might not always be the "best" model from a


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44

geological perspective. In general, the most prudent approach is to choose

the model at the iteration after which the RMS error does not change

significantly. This usually occurs between the 3

rd

and 5

th

iterations.

The data analysis and modeling procedure is explained as follows:

1. Calculation the resistivity values () for all readings and saving as

text or notepad file.

2. Input data file to the RES2DINV or RES3DINV software, which use

in interpretation as a notepad or text file.

3. Inspection of the resistivity data sets for presence of unreasonable

high and low (negative) resistivity values are also called " bad data

points " and remove of these bad data points that by "Exterminate bad

datum points " option as shown in figure(3.11).

4. Plotting the sensitivity of the blocks used in the inversion model by

displaying Model sensitivity option, shown in figure (3.12).

5. Displaying inversion result: in this option we can read data file, the

measured, calculated apparent resistivity pseudo-sections, and the

model section, figure(3.13).

6. Displaying inversion result after displaying the Robust model

inversion: in this option a model with sharp interfaces between

different regions with different resistivity values will be produced, as

shown in figure (3.14).


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Figure 3.11: Exterminating bad datum pointsoption,for inspecting the

resistivity data sets.

Figure 3.12:Model sensitivity option.


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Figure 3.13: The apparent resistivity pseudo-section for data set.

Figure 3.14: Inversion results show the effect of the Robust inversion.

3.2.6 Instumentation and Field work

3.2.6.1 Instrumentation:

High resolution 2D electrical resistivity tomography profiles using ARES

imaging resistivity meter was employed to assess horizontal and vertical

variations in resistivity across the study area. The resistivity meter is

available at the Department of Earth & Environmental Science, Yarmouk

University. It is equipped with 48 electrodes that can be connected

simultaneously with an inter-electrode spacing of up to 5 meters

(Figure3.15).


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Figure 3.15: ARES - Automatic Resistivity System having 4 passive

multielectrode cables with a total of 48 channel takeouts for electrical

resistivity tomography/imaging Surveys.

3.2.6.2 Field work:

Resistivity imaging profiles were carried out in the study area during June

2011. Both Wenner and Schlumberger resistivity arrays have been acquired

across the same profiles on different sides, orientations, and lengths across

the study area. This approach was found to be the most approperiate method

for solving the archaeological problems under consideration at the site.

Resitivity data acquisition including both types of measurements took

approximatly 2 hours to complete after cables and electrodes were laid out.

Each line required 4 cables, each with 12 electrode take-outs.


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The field measurements of the resistivity tomography were taken as follows:

1. Electrical profiles were designed and lain down based on field

observations and minimum field obstacles. The total length of all

profiles was determined according to the required estimated depth

of current penetration.

2. The coordinates of each profile were determined by using GPS.

3. Forty eight electrodes were planted and cables were used to

connect them with the instrument, the Automatic Resistivity

System (ARES).

4. Each profile was measured using the Wenner and Schlumberger

tomography configurations.

5. The displayed measurements were recorded and multiplied by its

geometrical factor (depends on spacing) to obtain the apparent

resistivities, which were used later in the analysis and

interpretation, according to the (eq.6 & eq.8) for Wenner &

Schlumberger arrays, respectively.


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Chapter Four

Results &

Discussion


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4.1 Results and Discussion:

The following section will present the results and the interpretation of the

subsurface encountered within the study area by using the two geophysical

techniques. The study area was subdivided into four parts of interest; the

eastern side part, the western side part, the northern side part, and within

pool part (Figure 4.1). Accordingly, for each method the presentation of

results will be provided for each individual station.

:The Western Side Area

The western side Area, as shown in Figure 4.1, is delimited between

(772392.266 E-3277350.867 N) and (772403.007 E-3577351.286 N) in its

northern part and between (772386.965 E-3577259.499 N) and (772399.938

E-3577259.359 N), in its southern part of the area assuming the UTM, Zone

36 coordinate system.

A total number of 4 profiles (L1W-L4W) were collected where each of the

profiles has a length of 94m and all were running from north to south. The

1

st

profile is adjacent to the pool Located at 1m from its western edge. The

distance between collected profiles is 1m. The observed apparent resistivity

pseudosections for the collected data using Wenner & Schlumberger

techniques are shown in figures 4.2 and 4.3, respectively.


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Figure 4.1: Illustrates the location of all stations in the area of the study, (Google

Earth, 2011).


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Figure 4.2: The observed apparent resistivity pseudosections for the collected

data of(L1W-L4W) profiles by using Wenner.


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data of(L1W-L4W) profiles by using Schlumberger.

The results of electrical resistivity tomographic using the two techniques are

shown in figures 4.4 and 4.5, respectively. The detailed inversion results are

given in appendix (A). The Schlumberger survey shows a deeper depth of

penetration when compared to Wenner pseudosections. However, these

subsurface models show a variation in their resistivity ranges from about (22.6

.m) to (324.m) for Wenner, and from about (18.5.m) to (397.m) for the

.Schlumberger


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Pseudosections of Wenner and Schlumberger show variability in the distribution

of resistivity defining three zones of anomalies of high resistivity values (Figures

4.4 and 4.5). These anomalies are designated as Anomaly (A) located between

(18-25.5m), and Anomaly (B) located between (34-40m) and Anomaly (C)

located between (54-56.5m), from the beginning of the sections.

In figure 4.4, the resistive zone of Anomaly (A) is buried at 2m from the surface

and it extends down to a depth of 4.5m. Similarly, Anomaly (B) is located at a

depth of 2-5.5m, while Anomaly (C) is found at a depth of 1.5-3m from the

surface. However, it is important to mention that other small anomalies may

exist, but they show lower resistivity values or poor imaging.

To the east, the extent of these anomalies shows very slight variabilities, such

that the anomalies (A and B) are not well characterized relative to that shown as

we move to the west away from the western edge of the pool (Figures 4.4 and

4.5). This may suggest the fact that restoration activities took place during the

sixties of the last century, carried out by the Engineering Corps of the Armed

Forces did not take into consideration the possibilities of the existence of

adjacent components or elements to the pool body. Unfortunately,

documentation of the restoration activities is missing.


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The results of the tomographic sections along the western area (figures 4.4 and

4.5), coupled with field observation indicated that the seen anomalous resistivity

values are greater than 200 and up to 397.m, may be interpreted as part of

ancient buried channels or supporting basins feeding or draining water out the

two water reservoirs. While the resistivity values range from 200.m to about

70.7.m are interpreted as weathered or fresh bedrock. The material of

resistivity values less than 70.7.m to 18.5.m may be associated with the

presence of a mixture of soils and conductive porous wet-alluvium surface

deposits.

In order to characterize the edges of the seen anomaly structures, the robust

inversion option was used. It has the ability to characterize abrupt high

resistivity contrasts between adjacent subsurface bodies due to any expected

sharp boundary (Claerbout and Muir, 1973). Figure 4.6 shows the inversion

result of Wenner resistivity tomography data for the 3rd

profile (L3W) using the

robust inversion option. It is quit evident that the previously defined anomalies

are strongly associated with structures of straight edges existing at right angles.

.


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Figure 4.4: Inverted resistivity data for the four parallel profiles (L1W-L4W) of

the western side area using Wenner. L1W is the closest line to the pool. The

letters (A, B, and C) highlight the highest resistivity values anomalies.


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Figure 4.5: Inverted resistivity data for the four parallel profiles (L1W-L4W) of

the western side area using Schlumberger. L1W is the closest line to the pool.

The letters (A, B, and C) highlight the highest resistivity values anomalies.

Figure 4.6: The inversion result of Wenner resistivity tomography data of the 3rd

line of the Western Side Area (L3W) using the robust inversion option. The high

contrasted bodies are selected by black rectangles.


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Although the pseudosections can already give some information about the

locations of subsurface structures, their lateral extensions cannot be correctly

visualized. Thus, 3D inversions of the measured data using the RES3DINV

software was performed, by emerging all measured data sets, in order to obtain a

more realistic image of the expected man-made structures. Practically, the

subsurface was divided into several layers, and each layer was subdivided into a

number of rectangular blocks.

Figure 4.7, shows the extracted horizontal depth slices from the inverted data of

Wenner resistivity tomography survey by emerging all measured data sets of the

western side area. It was concluded that there is a need to run a 3D ERT

acquisition exercise to the western side of the pool to confirm these initial 3D

inversion results. Therefore, another 3D survey across this side area and centered

above the expected location of Anomaly (B) was carried out. The dimensions of

the survey were 18 x 8m, such that the cable was run in a zigzag pattern with

interelectrode spacing of 2m along each raw and with a spacing of 1m between

adjacent parallel rows (Figure 4.8). The survey is composed of a set of 9

Schlumberger profiles in the x dimension (N-S), each with 10 electrodes.

The inverted data confirms the location of Anomaly B. It shows an extent of

subsurface structure of high resistivity values (561-861ohm.m), from about 0.5m

to 3.5m. Another anomaly of high resistivity values was detected, denoted by N,


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extending from about 1.5m to reach 2m (figure, 4.9). The expected subsurface

structures denoted by black rectangles are detected as a high resistivity values

anomalies (about 341ohm.m) and extend vertically to about 5m in layer 5.

Figure 4.7: The 3D-Wenner resistivity model of the western side area as

horizontal slices at varying depth using the RES3DINV software.


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Figure 4.8: 3D Electrical Resistivity Survey at the Western Side Area


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Figure 4.9: The Schlumberger electrical resistivity inverted slices obtained by

means of the application of RES3D software. Each slice refers to a layer with a

depth range. The expected subsurface structures are detected as high resistivity

values anomaly (561-861ohm.m), extending from about 0.5m to 3.5m in layer 7.

Another structure was detected by these inverted data denoted by N. It begins to

appear from about 1.5m to reach 2m.


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Figure 4.10: Created subsurface model for the Western Side Area.


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:The Northern Side Area

The northern side area is divided into two parts (A and B), as shown in Figure

4.1.

:The Northern Side Area A

Area A is delimited between (772386.635E-3577419.38N) and

(772444.065E-3577424.11N) in its northern part and between (772391.815E-

3577365.779N) and (772449.02E-3577368.707N) in its southern part

assuming the UTM, Zone 36 coordinate system.

Pair of profiles (L1-L2) runs from east to west were collected, and almost

normal to other three N-S profiles (L3-L5) running from north to south,

having a length of 48m. Slight shifts were done due to existing field obstacles.

A total spacing of ten meters is taking place between all measured lines. At

the southern edge of Area A, another 2 profiles (L6-L7) were run having a

length of 48m (shown in green color on figure 4.1).

The observed apparent resistivity pseudosections for the collected five normal

to each other profiles (i.e. brown and yellow lines shown in figure 4.1), using

Wenner & Schlumberger techniques, are shown in figures 4.11 and 4.12.


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Figure 4.11: The observed apparent resistivity pseudosections for the

collected data of (L1-L5) of the Northern side area A by using Wenner .


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Figure 4.12: The observed apparent resistivity pseudosections for the

collected data of (L1-L5) of the Northern side area A by using Schlumberger .


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The results of electrical resistivity tomographic inversion using the two

techniques are shown in figures 4.13 and 4.14, respectively. The detailed

inversion results are shown in appendix (C). The Schlumberger survey shows

a deeper depth of penetration when compared to Wenner pseudosections.

Wenner and Schlumberger subsurface models show a variation in their

resistivity ranges from about (25.7 .m) to (269.m) for Wenner, and from

about (20.6.m) to (302.m) for the Schlumberger. They are characterized

with 5 distinct anomaly zones of higher resistivity values. In the N-S sections,

Anomaly (A) is located between 25.5 to 32m, and Anomaly (B) is located

between 36.5 to 41m, while in the E-W sections, Anomaly (C) is located

between 8 to 11m, and Anomaly (D) takes place between 27 to 31.5m, from

the start of each section (Figures 4.13, and 4.14). The fifth anomalous zone is

seen along the topmost part of the sections characterizing the uppermost part

of the section down to a depth of 0.5m. Additionally, these inverted sections,

show that the vertical extensions for these anomalies are delimited between

3.5 to 5.5m , 4 to 5m, 3 to 4m and 3 to 5.5m for the anomalies of A, B,C and

D, respectively.

The results of the inversion process are strongly supporting the conclusion

that attained 4 anomalies of high resistivity values ranging from greater than

130ohm.m to 302ohm.m (A, B, C and D) which can be potentially

interpreted as a part of a general infra structure of ancient man-made buried

channels or supporting basins feeding water to the two water reservoirs. These


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structures are cut within existing limestone bedrock showing resistivity

ranging between 130ohm.m to 65.1ohm.m. This anomalous zone is buried

under a layer or slab of fill material characterized by much lower resistivity

values (less than 65.1ohm.m to 20.6ohm.m). Comparing the pseudosections

of the E-W and N-S profiles shows the compatibility between their results.

The anomaly (D) in the E-W profiles can be correlated with the anomaly (A)

in the N-S profiles.

On the other hand, the other high resistivity part that extends along the

topmost of the sectionsis interpreted as a 0.5 meter pavement floor. The fact

that this zone is characterized by a distinguished uniform lateral continuity

and elevated resistivity values, in addition to continuous fill layer material

laying below strongly supporting this conclusion (Figures 4.13, and 4.14).

Down to the south, another pair of E-W lines (L6 &L7) was collected using

both Wenner and Schlumberger techniques. Forty-seven meters profiles were

located parallel to the E-W pair of profiles.

The observed apparent resistivity pseudosections for the collected data using

Wenner & Schlumberger techniques are shown in figures 4.15, and 4.16,

respectively. The inverted data result (Figures 4.17, and 4.18) show the

continuity of the lateral extent of the pavement layer shown by the previous

inverted sections of the northern part of this area. The characteristic layering

is very similar to the previous sections, where a characteristic conductive fill

material is buried under the pavement layer for leveling purposes. The


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pavement layer shows anomalous high resistivity values of more than 200

.m. Additionaly, a characteristic step was seen across the two sections

almost 32m from the start of the sections, suggesting that the elevation of the

northern part of this area was higher, where dwellers or visitors used to

descent or step down to the lake as they approach from North to south. The

inverted data of the L7 profile detect high resistivity values anomaly of more

than 200 .m (denoted by E) extending from 36 to 37m from the start of the

section.

Figure 4.13: Presents the resulting of Wenner inverted data for (L1-L5), of the

Northern side area A. The letters (A, B, C and D) highlight the highest


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resistivity values anomalies. The two directions sets of profiles have a

crosscut points denoted by a small black circles shown in the figure.

Figure 4.14: Presents the resulting of Schlumberger inverted data for (L1-

L5), of the Northern side area A. The letters (A, B, C and D) highlight the

highest resistivity values anomalies. The two directions sets of profiles have a

crosscut points denoted by a small black circles shown in the figure.


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Figure 4.15: The observed apparent resistivity pseudosections for the collecteddata of the L6 profile. The upper section is by Wenner, and the lower one is by

Schlumberger.


data of the L7 profile. The upper section is by Wenner, and the lower one is by

Schlumberger.


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Figure 4.17: The inverted resistivity data results of the L6 profile. The upper

section is by Wenner, and the lower one is by Schlumberger. The topmost part

of the upper section indicates to an expected pavement layer.

Figure 4.18: The inverted resistivity data results of the L7 profile. The upper

section is by Wenner, and the lower one is by Schlumberger. E is high

resistivity values anomaly. The topmost part of the upper section indicates to anexpected pavement layer.


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Figure 4.19: Created subsurface model for the Northern Side Area A.

Figure 4.20: Electrical Resistivity Survey at the Northern Side Area A.


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The Northern Side Area B:

Area B is delimited between (772400.824E-3577362.851N) and (772449.921E-

3577363.301N) in its northern part and between (772400.598E-3577358.572N)

and (772449.921E-3577359.247N) in its southern part of the area assuming the

UTM, Zone 36 coordinate system.

A total number of 3(L8-L10) profiles were collected each of the profiles has a

length of 47m running from east to west with an inter-line distances of one

meter. The observed apparent resistivity pseudosections for the collected data

using Wenner & Schlumberger techniques are shown in figures 4.21 and 4.22,

respectively.

The results of electrical resistivity tomography using the two techniques are

shown in figures 4.23 and 4.24, respectively. The detailed inversion results are

shown in appendix (D).

The inverted Wenner and Schlumberger sections show clear variability in the

distribution of resistivity values within the subsurface. The upper most part of

the sections show segregated zones of higher resistivity values400-854ohm.m on

figures 4.23 & 4.24. The fact that these zones are underlain by the same fill layer

material seen in previous sections, strongly suggest that these zones are relicts of


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the ancient pavement floor surrounding the pool body. The zone of the image

with resistivity values ranging from 74.1ohm.m to less than 400ohm.m indicates

weathered and fresh bedrock. The zone of resistivity values from 13.4ohm.m to

less than 74ohm.m is a mixture of soils and conductive porous wet-alluvium

deposits.


data of (L8-L10) of the Northern side area B by using Wenner .


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data of (L8-L10) of the Northern side area B by using Schlumberger .


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Figure 4.23: The inverted resistivity data results of ( L8-L10) profiles, by using

Wenner. The anomalies A,B, and C highlight high resistivity values anomalies.

Figure 4.24: The inverted resistivity data results of ( L8-L10) profiles, by using

Schlumberger. The anomalies A and B highlight high resistivity values

anomalies.


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Figure4.25: Created subsurface model for the Northern Side Area B.

Figure 4.26: Electrical Resistivity Survey at the Northern Side Area B.


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:The Eastern Side Area

The eastern side area, as shown in Figure 4.1, is delimited between

(772449.056E-3577361.073N) and (772473.369E-3577361.333N) in its northern

part and between (772447.366E-3577266.164N) and (772475.449E-

3577266.164N) in its southern part of the area assuming the UTM, Zone 36

coordinate system.

A total number of 4 profiles (L1E-L4E) were collected, each of the profiles

having a length of 94m that runs from north to south. The 1st

profile is adjacent

to the pool, located at 1m from its eastern edge. The spacing between the

collected profiles is 1m.

The observed apparent resistivity pseudosections for the collected data using

Wenner & Schlumberger techniques are shown in the figure 4.27 and 4.28,

respectively. The results of electrical resistivity tomography using the two

techniques are shown in the figures 4.29 and 4.30, respectively. The detailed

inversion results are shown in appendix (B).

The inversion results of the Wenner and Schlumberger surveys show number of

anomalies; Anomaly (A) occurring at 35-38 m, anomaly (B) located at 58-72m,

and anomaly (C) located at 80-94m, from the beginning of each section. The 3


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anomalies are well characterized across the 4 lines, except for anomaly (A)

which is poorly distinguished across the 2 profiles (L3E & L4E).

These models draw variation of resistivity ranges from about 10.3.m to

377.m in Wenner and from 11.6.m to 384.m in Schlumberger. In figure

4.29, the resistive zones, on A of the image, is almost under 0.25m to reach 2m

in depth, about 2-4m on B & C. To east, the vertical extension of these

anomalies appears to be disparate. In figure 4.30, the anomaly zone on A of the

image is almost from 0.25m to 2m in depth, and it is about 1.5-4m on B&C. To

the east, the vertical extension of these anomalies appears to be disparate.


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Figure4.27: The observed apparent resistivity pseudosections for the collected

data of (L1E-L4E) profiles of the Eastern side area by using Wenner .


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Figure4.28: The observed apparent resistivity pseudosections for the collected

data of (L1E-L4E) profiles of the Eastern side area by using Schlumberger.

The inverted models are assumed to represent the same geology. The resulting of

Wenner tomographic image along the eastern side area is presented in figure

4.29. Similar to the western side area interpretations, field observation indicated

that the A, B, and C high resistive zones from 200.m -384.m may be

interpreted as ancient buried structure of channels or supporting basins feeding

or draining out the two water reservoirs. While the resistivity values ranging

from 50.m to less than 200.m can be interpreted as weathered-fresh bedrock,


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materials having resistivity values less than 50.m can be interpreted as a mix of

soils and conductive porous wet-alluvium deposits.

The robust inversion technique was used due to its ability to show the high

resistivity contrast for different subsurface bodies and any expected sharp

boundary. Figure 4.30 shows the inversion result of resistivity tomography data

using the robust inversion technique.

Although the pseudosections can already give some information about the

locations of subsurface structures, their size, depth and extent cannot be correctly

estimated. Thus, 3D inversions of the measured data using the RES3DINV

software were performed, by emerging all measured data sets, in order to obtain

a more realistic image of the expected man-made structures. Practically, the

subsurface was divided into several layers, and each layer was subdivided into a

number of rectangular blocks. Figure 4.31, shows the extracted horizontal depth

slices from the inverted resistivity tomography data by emerging all measured

data sets of the eastern side area.

As seen across the figures 4.29 and 4.30, anomlay (B) can be considered as the

major structures taking place across the eastern side area, accordingly it was

imoport to test the E-W continuity of this anomaly. An intention of conducting

3D data directly by the ARES instrument to detect the shallow anomalous zone


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with dimension of some meters detected previously in the 2D results was in

mind, but the amount of space was not available to layout this. Additionaly,

Existing field obsticales hindered our quest to rub 3D resititvy acquiztion,

therefore a dicision was made to run a typical 2D line runing normal to the three

N-S sections presented previously.

A perpendicular E-W line (L5E) of 23.5m long and 0.5m electrodes spacing was

run to predict the eastern extension of the main anomaly denoted by B. It's end

crosscuts other N-S line of 23.5m (L6E), at 7m. The observed apparent

resistivity pseudosections for the collected data using Wenner & Schlumberger

techniques and the results using the two techniques are shown in the figures 4.33

& 4.34, and, 4.35 & 4.36 for L5E and L6E respectively. The detailed inversion

results are shown in appendix (B).

The inverted data of L5E profile did not show any further extension of the

anomalous zone (B) after the first four meters from the eastern edge of the pool.

L6E's inverted data show two anomalies of high resistivity values, one at the first

4m, and the second is from about 8 to 10m from its start.


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Figure 4.29: Parallel pseudosections of electrical resistivity values of the Eastern

side area using the Wenner tomography survey. L1E line is the closest to the

pool. A, B, and C, all highlight the highest resistivity values anomalies.


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Figure 4.30: Parallel pseudosections of electrical resistivity values of the Eastern

side area using the Schlumberger tomography survey. L1E is the closest to the

pool. A, B, and C, all highlight the highest resistivity values anomalies.

Figure 4.31: The inversion result of Wenner resistivity tomography data of the

4th

profile of the Eastern Side Area (L4E) using the robust inversion option. The

high contrasted body is selected by black rectangle.


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i

Figure 4.32: The 3D-Wenner resistivity model of the eastern side area as

horizontal slices at varying depth using the RES3DINV software. The

expected subsurface structure denoted by a black rectangle are detected as

a high resistivity value anomalies (about 419 ohm.m) and begins

appearing at depth 3.4-4.99m in layer 5.


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ii

Figure4.33:The observed apparent resistivity pseudosection for the

collected data of (L5E) at the upper part, and the inverted data result of

(L5E) at the lower part. By using Wenner.

Figure4.34:The observed apparent resistivity pseudosection for thecollected data of (L5E) at the upper part, and the inverted data result of

(L5E) at the lower part. By using Schlumberger.



(L6E) at the lower part. By using Wenner.


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(L6E) at the lower part. By using Schlumberger.

Figure 4.37: Created subsurface model for the Eastern Side Area.


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iv

Figure 4.38: Electrical Resistivity Survey at the Eastern Side Area.

Within the pool area

There was a need to survey the area within the pool area in order to have

an idea about the structure of the pool itself. Since the pool structure is

selected within the valley plain of Wadi AL-Dair, it was important to

know more about the foundation material of the pools. It was important

the understand whether pools body was cut into the bedrock, or was

there major earthworks to fill and level or possibly pave the bottom of the

two pools?


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Figure 4.39: Electrical Resistivity Survey within the pool.

A total number of 4 profiles (LP1-LP4) were collected as two pairs

(Figure 4.1). The E-W pair of profiles (LP3-LP4) has a length of 42m and

runs from east to west with a line spacing of 16m. While the N-S pair of

profiles has a length of 47m and runs from north to south with line

spacing of 20m.

The observed apparent resistivity pseudosections for the collected data

using Wenner & Schlumberger techniques are shown in figures 4.40 and

4.41, respectively. The results of electrical resistivity tomography using

the two techniques are shown in figures 4.42 and 4.43, respectively. The

detailed inversion results are shown appendix (E).


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The inverted Wenner and Schlumberger section show an almost

continuous zone of anomaly of high resistivity values along the topmost

part of the sections. The resistive zone does not exceed a general depth of

1m.

The results of inversion indicates that this anomalous zone (>475 -

1106.m) gives rise to a realization that the bottom of the pond was

paved by a layer limestone pavement of a thickness of 1 meter. The

pavement is underlain by a thick sequence of wadi sediments and

sediment fill material, which is believed to be evenly leveled. However,

this conclusion keeps it open to think about the possibility that localized

outcrops may be present within the floor of the pools, which was

integrated within the intruded pavement material. Localized outcrops

were seen along the NW and SW corners of the pools floor (Figure

4.44). Therefore, the fill materials having resistivity values ranging from

13.3.m to about 46.9.m are a mixture of soils and conductive porous

wet-alluvium deposits.


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Figure4.40:The observed apparent resistivity pseudosections for the

collected data of (LP1-LP4). By using Wenner.


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Figure4.41:The observed apparent resistivity pseudosections for the

collected data of (LP1-LP4). By using Schlumberger.


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Figure 4.42: Pseudosections of electrical resistivity values of the within pool area

using the Wenner survey across the bottom of the northern pond showing a clear

pavement of 1m thick layer.


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Figure 4.43: Pseudosections of electrical resistivity values of the within pool area

using the Schlumberger survey across the bottom of the northern pond showing a

clear pavement of 1m thick layer.


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Figure 4.44: Localized outcrop at the S-W edge within the pool.


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Figure 4.45: Created subsurface model within the Pool body.

conclusion:-Sub

After looking for what many authors said about the site of Al-Berktain

(e.g. Kraeling, 1938 & Segal, 1995), and what the results of this study

showed, doubtless the conscious policy from DoA and the ministry of

tourism is important to revive and protect this archaeological site from

neglect.

Al-Berktain was a main source for supplying the western part within the

wall of the ancient Jerash with water. "Ain Qarawan is a perennial spring

within the walls, but it lies too low in the valley to provide water for the

western part of the ancient Jerash. Water was, therefore, channeled from


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Al-Berktain (two water reservoir)", (Kamash, 2009). This study gave an

idea about the ancient architecture of the site; the rectangle lake is almost

surrounded from E and W by water channels as inlets and outlets. The

elevation level of the northern part of the site was higher, where visitors

used to step down to the lake that gave the site a remarkable character.


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Chapter Five

Conclusions &

Recommendation


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Conclusions5.1

From the present study, it can be concluded that:

1- The combination applications of Wenner tomography and

Schlumberger tomography data produces stronger anomalies compared

to either method used individually.

2- By plotting the data sets on the same scale, the results produce

reasonable data correlations and interpretations; the combining of the

both methods data minimizes the ambiguities in the interpretation and

allows the location of possible buried archaeological remains in the

first meters of the subsoil. If only a single method to be used, Wenner

is best for detection the expected archaeological remnants due to its

greater signal strength, while Schlumberger gives deeper image of the

subsurface.

3- The proposed method of the 3D visualization confirms the

interpretation of the 2D sections, and allows the best recognition of

archaeological features.

4- The results proposed for each side area are as follow:

The Northern side A:

The results of the inversion process show that anomalous resistivity

values are interpreted as a part of a general infrastructure of ancient man-

made buried channels or supporting basins feeding water to the two water


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reservoirs. This anomalous zone is buried under a layer of fill material.

The fill material is overlain by a continuous layer of pavement (i.e. of

0.5m thickness) that was seen along N-S and E-W intercrossing 2D ERT

profiles.

The Northern side B:

The results of the inversion process indicate the presence of an ancient

pavement floor surrounding the pools' body covering mixture of soils and

conductive porous wet-alluvium deposits and weathered and fresh

bedrock.

The Eastern Side Area:

The results of the inversion process interpret the highest resistivity values

as ancient buried structure of channels or supporting basins feeding or

draining out the two the water reservoirs, underlain by a mix of soils and

conductive porous wet-alluvium deposits, and weathered or fresh

bedrock.

The Western Side Area:

The results of the inversion process interpret the highest resistivity values

as part of ancient buried channels or supporting basins feeding or

draining water out the two water reservoirs underlain by a mix of soils

and conductive porous wet-alluvium deposits, and weathered or fresh

bedrock. The 3D survey carried out across the 2D seen resistivity


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anomaly indicated the presence of a well-defined anomalous extension to

the west.

The in-Pool Side Area:

The results of inversion process show that a characteristic thin anomalous

zone of the highest resistivity values can be interpreted as a limestone

layer pavement of 1 meter thickness flooring the bottom part of the pools.

The pavement is underlain by a thick sequence of wadi sediments and

sediment fill material. Localized outcrops were seen along the NW and

SW corners of the pools floor, and show a zone of fill materials mixture

of soils and conductive porous wet-alluvium deposits.

Table 2 summarizes the results of this survey. The buried findings arrived

to 5.5meters under the surface located around the pool body. They are in

a relationship with the location of the pool body (figure 5.1)


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Table 2: Summary of the results of the ERT survey at Al-Berktain site.

Resistivity

values

(ohm.m)

Thickness

(m)

Vertical

extension (m)

Lateral

extension (m)

Anomaly

200-397

7.52-4.518-25.5AWesternside area

62-5.534-40B

2.51.5-354-56.5C

200-384

30.25-235-38AEastern

side area 141.5-458-72B

141.5-480-94C

130-302

6.53.5-5.525.5-32ANorthern

side area(A)

4.54-536.5-41B

33-48-11C

4.53-5.527-31.5DAbout 0.5 m pavement floor, with resistivity values ranging 200-397 ohm.m

Segregated anomalies described as relicts of ancient pavement floor (0.6-1m), with

resistivity values ranging 400-854 ohm.m

Northern

side area

(B)

About one meter of pavement floor almost between 0.12m1.1m, with resistivity

values greater than 200 o

Documents

Integrated Application of Geophysical Methods in Archaeology