Gad El-Qady

2-D inversion of VES data in Saqqara archaeological area, Egypt

The interpretation of actual geophysical field data still has a problem for obtaining a unique solution. In order to investigate the groundwater potentials in Saqqara archaeological area, vertical electrical soundings with Schlumberger array have been carried out. In the interpretation of VES data, 1D resistivity inversion has been performed based on a horizontally layered earth model by El-Qady (1995). However, some results of 1D inversion are not fully satisfied for actual 3D structures such as archaeological tombs. Therefore, we have carried out 2D inversion based on ABIC least squares method for Schlumberger VES data obtained in Saqqara area. Although the results of 2D cross sections were correlated with the previous interpretation, the 2D inversion still shows a rough spatial resistivity distribution, which is the abrupt change in resistivity between two neighboring blocks of the computed region. It is concluded that 3D interpretation is recommended for visualizing ground water distribution with depth in the Saqqara area.

Integrated Geophysical Survey for Site Investigation at a New Dwelling Area, Egypt

An integrated geophysical survey was carried out in a new dwelling area at 15-May town, southeast Cairo, Egypt. The buildings in this area are intensively affected by dangerous cracks that cause structural instability. The survey aimed to image the shallow subsurface structures, including karstic features, and evaluate their extent, as they may cause rock instability and lead to cracking of the residential buildings. Resistivity profiling (2-D), using a dipole-dipole array and ground penetrating radar (GPR) surveys were carried out along seven parallel traverses extending about 150 meters between the buildings blocks. Additional measurements using a Schlumbereger array and very low frequency electromagnetic (VLF-EM) methods were conducted. The acquired data were processed and interpreted integrally to elucidate the shallow structural setting of the site. Integrated interpretation led to the delineation of hazard zones rich with karstic features in the area. Most of these karstic features are associated with vertical and sub-vertical linear features such as faults, fracture zones, and geologic contacts. These features are the main reason of the rock instability that resulted in potentially dangerous cracking of residential buildings.

Tracing buried pipelines using multi frequency electromagnetic

Abstract In this paper the application of multi frequency electromagnetic techniques to locate buried pipelines is described. The survey site has two pipelines of SUMED, one of the world chokepoints. At desert or arid areas, regular geophysical surveys usually are difficult to carry out. EM techniques could be the best among geophysical techniques to be used for this target at these conditions. The EM survey was performed using a GEM-300 multi-frequency electromagnetic profiler. It is of handheld electromagnetic induction-type that measures in-phase and quadrature terrain conductivity without electrodes or direct soil contact. An area of 60 × 15 m was surveyed, that supposed SUMED pipeline existed. Six different frequencies, typically 2025, 2875, 4125, 5875, 8425, 12,025 Hz, have been used simultaneously. The slice maps for in-phase and conductivity distribution at each frequency could help to trace the extension of the pipeline. Two pipelines were traced successfully with 20 m spacing of each others.

Hydrogeophysical Investigations at El-Nubariya-Wadi El-Natrun Area, West Nile Delta, Egypt

Establishing new communities is one of the strategic plans of the Egyptian government during the last decades. One of the targeted localities for such plan is the West Nile Delta area where it is considered as a promising area for creating new settlements. The area under investigation is located to the west of Nile Delta on both sides of the Cairo-Alexandria desert road, between latitudes 30° 17′ and 30° 42′ N and longitudes 30° 00′ and 30° 30′ E. It covers an area of about 1,825 km2. To help such national plan, the present study aims to delineate the hydrogeological regime of the study area through qualitative and quantitative interpretation of the available electrical and electromagnetic data.

Hydrogeophysical and structural investigation using VES and TDEM data: A case study at El-Nubariya–Wadi El-Natrun area, west Nile Delta, Egypt

Abstract The geoelectric survey includes 93 Vertical Electric Soundings (VES) and 26 TEM stations were conducted to delineate the subsurface structures and hydrogeological regime of El-Nubariya–Wadi El-Natrun area. The VESes AB/2 was varying from 1 up to 700 m in successive steps, while TEM stations were measured using coincident loop of 50 m side length. The interpretation of the geoelectrical data shows that the depth to the main aquifer ranges from 6 m at the northern part near the Nubariya city to about 90 m at the southern parts where it increases to the south and southeast directions. Generally the aquifer system in the area can be divided into Pleistocene and Pliocene aquifers. The Pleistocene aquifer is the shallower aquifer in the area and it consists almost of gravelly to clayey sand deposits. The Pliocene aquifer is the main aquifer where it is composed of sand to gravelly sand deposits. Depending on the results of the geoelectric prospecting represented by the true resistivity map, we can infer the quality of the groundwater. A brackish groundwater can be found at the northern and northeastern parts of the study area at shallow depths whereas relatively fresh water can be detected at the southern and southeastern parts around Wadi El Natrun city at deep depths. The area under consideration is affected by a group of normal faults that divided the investigated area into five main divisions, northern, eastern, western, southern and central divisions. The inferred faults from the geoelectric sections are traced and collected to construct a structure map. It is worth to mention that Wadi El Natrun and its lakes are structurally controlled by faulting systems trending NW direction.

Shallow groundwater investigation using time-domain electromagnetic (TEM) method at Itay El-Baroud, Nile Delta, Egypt

Abstract The Nile Delta is one of the oldest known ancient delta, largest and most important depositional complex in the Mediterranean sedimentary basin. Furthermore, it is a unique site in Egypt that is suitable for accumulation and preservation of the Quaternary sediments. In this work we applied time-domain electromagnetic (TEM) method to investigate the Quaternary sediments sequence as well as detecting the groundwater aquifer in the area of study. A suite of 232 TEM sounding at 43 stations were carried out using a “SIROTEM MK-3” time-domain electromagnetic system. A simple coincident loop configuration, in which the same loop transmits and receives signals, was employed with loop side length of 25 m. The 1-D modeling technique was applied to estimate the depth and the apparent resistivity of the interpreted geoelectrical data. Based on the interpretation of the acquired geophysical data, four geoelectric cross-sections were constructed. These sections show that the Upper Quaternary sequence consists of three geoelectric layers. The Holocene Nile mud is separated into two layers: the agricultural root zone (Layer 1) and thick water saturated mud (Layer 2). The Upper Pleistocene sandy aquifer (Layer 3) is very complicated non-linear boundary. This aquifer is the most important unit since it is considered as the main water bearing unit in the study area.

A Coastal Aquifer Study Using Magnetotelluric and Gravity Methods in Abo Zenema, Egypt

Magnetotelluric (MT) soundings and gravity methods were employed to study the deep freshwater aquifer in the area north of Abo Zenema city on the eastern side of the Gulf of Suez, Egypt. Seven MT sites and 48 gravity stations were surveyed along northeast–southwest profiles as close as possible to a line perpendicular to the coast of the Gulf of Suez. The MT survey was conducted using high and low frequencies to investigate shallow and deep areas, respectively. One-dimensional inversion was conducted using a heuristic inversion scheme of the Bostick algorithm. The MT data were also inverted with a 2-D smooth model inversion routine using the nonlinear conjugate gradient method to infer variation in vertical and lateral resistivity inside the Earth. A 100-Ohm-m homogeneous half-space initial model was used to invert the TE mode data only. Then, the inverted model obtained from the TE mode data was used as an initial model for inversion of the TM mode data. The inverted model thus obtained from the TM mode data inversion was used as an initial model for the inversion of the joint TE and TM responses. Two-dimensional (2-D) forward modeling of the gravity data was conducted using the 2-D polygon method of Talwani’s algorithm for an arbitrarily shaped body and was based on the subsurface information from the MT survey and the available information about the geological structure of the study area. This method enabled us to obtain the basement structure of the coastal aquifer in the study area. The results from the analysis and the interpretation of MT and gravity data were used to detect and delineate the groundwater coastal aquifer in the study area.

Geophysical Techniques Applied in Archaeology

With the increased demand to facilitate the archaeological work either in well-known archaeological sites or the crude sites, geophysical methods plays an important role. The Geophysical methods have been used since 1946 with increasing frequency for archaeological investigations and currently the branch of archaeogeophysics is widely applied. The wide varieties of geophysical methods applied in archaeological work relies principally upon existing reasonable contrast in physical properties between the buried archaeological feature and the surrounding subsoil. Understanding the archaeological properties of the physical contrasts, in terms of density, thermal conductivity, electrical resistance, magnetic or dielectric properties, remains fundamental issues of choosing and applying the discipline geophysical techniques. In this regard, we tried to introduce a brief outline for the common and applicable techniques in archaeological investigations. The physical principles and field instrumentation involved for the acquisition of data with each method are considered, as well as some common results from the worldwide case studies. Generally, the archeogeophysical survey results can be used to guide excavation and to give archaeologists insight into the patterning of non-excavated parts of the site as well as it is often used where preservation of the sensitive sites is the aim rather than excavation.