Essam Aboud

Integrated gradient interpretation techniques for 2D and 3D gravity data interpretation

The Obama geothermal field is located on the western part of Kyushu Island, Japan. This area has importance due to its high geothermal content which attracts sporadic researchers for study. In 2003 and 2004, Obama was covered by gravity surveys to monitor and evaluate the geothermal field. In this paper, the surveyed gravity data will be used in order to delineate and model the subsurface structure of the study area. Gradient methods such as analytic signal and vertical derivatives were applied to the gravity data. The available borehole data and the results of the gradient interpretation techniques were used to model the Obama geothermal field. In general, the obtained results show that the gradient interpretation techniques are useful to obtain geologic information from gravity data.

Integration of DEM, ETM+, Geologic, and Magnetic Data for Geological Investigations in the Jifara Plain, Libya

We used an integrated approach to constrain the geological structure of the Jifara Plain in northwest Libya. The analysis of surface data, including a digital elevation model (DEM), Landsat Enhanced Thematic Mapper Plus images, and geologic maps, was combined with subsurface data, including well logs and magnetic data. The DEM data were used for the identification of geological lineaments in the study area. The interpretation and analysis of the lineaments indicate that the Jifara Plain is controlled by three main fault systems, trending northwest-southeast, east-west, and northeast-southwest. The three trends represent the remnants of reactivated structures that formed under the stress regimes generated during the tectonic evolution of North Africa. The magnetic data reveal three northwest- and northeast-trending sedimentary basins in the study area. The depth of the basement inside the main basin ranges from 1 to 5 km. The results indicate that the Jifara Basin is shallower than the surrounding basins. The integration of the results reflects different periods of tectonic activity in the Jifara Plain and the adjacent Jabal Nafusah.

Analysis and interpretation of gravity data from the Aluto-Langano geothermal field of Ethiopia

The Aluto-Langano geothermal field is located in the central southern portion of Ethiopia within the Ethiopian Rift Valley. The gravity of the area was surveyed in an attempt to delineate the subsurface structure and to better understand the relationship between the geothermal systems and the subsurface structure. The gravity data were analyzed using integrated gradient interpretation techniques, such as the Horizontal Gradient (HG), Source Edge Detection (SED), and Euler Deconvolution (ED) methods. These techniques detected many faults that were compared with the mapped faults in the surface geology. The results of the present study will lead to an improved understanding of the geothermal system in the study area and aid the future geothermal exploration of the area.

Integrating data from remote sensing, geology and gravity for geological investigation in the Tarhunah area, Northwest Libya

Abstract The present work deals with the integration of remote-sensing, surface-geology and gravity-survey data to improve the structural knowledge of the Tarhunah area, northwest Libya. Geological information and remote-sensing data provided information about the surface structure. A gravity survey was conducted to decipher the subsurface structure. The results revealed that a basin having a width of 39 to 48 km trends NE. A two-dimensional (2-D) schematic model shows that the basin gradually deepens toward the southwest. Faults determined from a horizontal gradient, tilt derivative, and Euler deconvolution show a depth range of 2.5 to 7.5 km. The integration and interpretation of the results indicate that volcanic activity was related to the tectonic activity of an anticlinal structure called the Jabal Uplift.

Mapping the depth to magnetic basement using inversion of pseudogravity: Application to the Bishop model and the Stord Basin, northern North Sea

Magnetic depth estimation methods are routinely used to map the depth of sedimentary basins by assuming that the sediments are nonmagnetic and underlain by magnetic basement rocks. Most of these methods generate basement depth estimates at discrete points. Converting these depth estimates into a grid or map form often requires the application of qualitative methods. The reason for this is twofold: first, in deeper parts of basins, there is generally a scarcity of depth estimates and those that have been determined tend to be biased toward the shallower basement structures close to the basin edge; and second, depth estimates intrinsically relate to magnetic anomalies that emanate from the top edges of basement faults/contacts resulting in a shallow depth bias. Thus, simple grid interpolation of these depth estimates often forms a shallower and structurally unrepresentative map when evaluated in detail. To overcome these problems of qualitative and/or simple grid interpolation of these point-depth estimates into a regular grid, we use the pseudogravity field transform response of the magnetic field to constrain this interpolation using inversion methods together with the relationship between the point-depth estimates and their pseudogravity values. The pseudogravity transformation converts a grid of magnetic data such that the resulting grid has the same simple relationship to magnetic susceptibility that a gravity grid has to density. The pseudogravity map is thus straightforward to visualize in terms of basement structure, but it only maps the magnetic properties of the subsurface and is not related to the gravity anomaly or the density. We describe a practical approach to invert pseudogravity grids using gravity inversion software to produce a 3D basin model assuming a constant susceptibility basement. The approach is initially tested on the Bishop 3D model and then applied to an example from the northern North Sea. This approach can be considered complementary to 3D gravity inversion and has the advantage that the pseudogravity response is not affected by structure within the sediments or effects such as sediment compaction, inversion, or isostatic compensation, all of which often complicate the gravity response of sedimentary basins.

Subsurface structural mapping of Gebel El-Zeit area, Gulf of Suez, Egypt using aeromagnetic data

The Gebel El-Zeit area is located on the western coast of the Gulf of Suez, Egypt. The areas in/and around the Gulf of Suez are generally important due to their hydrocarbon resources. In this study, we have applied gradient interpretation techniques (Euler deconvolution and analytic signal) to the aeromagnetic data of the Gebel El-Zeit area. The main objective of this study is to identify and delineate the possible subsurface structure of the area that may assist in locating new hydrocarbon prospects. Results of Euler method suggested that, on the eastern and western parts of the area, the basement could be observed on the ground (~50 m over the ground) and became more deeper on the central part to reach depth of 5 km (from the ground level). Results from the analytic signal method indicated that, the depth to the basement has an average value of 156 m on the eastern side and 758 m on the western side. Generally, the area is characterized by a graben structure bounded by major faults striking in the NW-SE direction.

Structural mapping of Quseir area, northern Red Sea, Egypt, using high-resolution aeromagnetic data

Exploration in the northern Red Sea of Egypt has had little success in locating hydrocarbon accumulation. The main exploration problems in this region are the complex block faulting and Miocene salt structures. The complex basement block structure arises from the different ages of faults and the difficulty of determining the exact age relations. In this paper, we present a case study of structural mapping using application of the Euler method to high-resolution aeromagnetic data collected in the Quseir area of the northern Red Sea of Egypt. The results indicated that the area is affected by sets of fault systems, which are mainly trending in the NNW-SSE, NW-SE and NE-SW directions. The results also delineated boundaries of a long and wide magnetic body on the offshore part of the study area. This basement intrusion is most probably related to the Red Sea rift and perhaps associated with structures higher up in the sedimentary section. As a result, the area above this anomaly is highly recommended for further oil exploration. This example illustrates that high-resolution aeromagnetic surveys can help greatly in delineating subsurface structure in the northern Red Sea of Egypt.

Investigating Structural and Tectonic Evolution of Central Afghanistan Using Remote Sensing and Gravity Data

This study used an integrated approach to investigate geological structure and tectonic evolution in Central Afghanistan. Several image processing techniques have been separately and simultaneously applied to data obtained from Landsat Enhanced Thematic Mapper Plus (ETM+) and Digital Elevation Models (DEM) to constrain the geological structure of the study area. Satellite images were combined with Gravity data to better understand 3D geology in the area. Analysis and interpretation of the extracted lineaments indicate that the Central Afghanistan area is controlled by two main fault systems, trending NE and EW. The two trends represent the remnants of reactivated structures that formed under the stress regimes generated during the tectonic evolution of Central Afghanistan. Gravity data indicate a NE trending basin. A two- dimensional (2D) schematic model shows that the basin deepens in the central area and gradually shallows towards the edges. The integration of the results gave insight into the tectonic evolution of the Central Afghanistan area and the adjacent areas.

Water exploration using Magnetotelluric and gravity data analysis; Wadi Nisah, Riyadh, Saudi Arabia

Abstract Saudi Arabia is a desert country with no permanent rivers or lakes and very little rainfall. Ground water aquifers are the major source of water in Saudi Arabia. In the Riyadh region, several Wadies including Wadi Nisah store about 14 × 106 m3 of water, which is extracted for local irrigation purposes. In such areas, the water wells are as shallow as 200–300 m in depth. The importance of Wadi Nisah is because the subsurface water aquifers that are present there could support the region for many years as a water resource. Accordingly, in this study, we performed a Magnetotelluric survey using a portable broadband sounding system (MT24/LF) to evaluate the ground water aquifer at great depths. We collected 10 broadband Magnetotelluric sounding stations (1 station/day) with an interval of about 2–3 km reaching a profile length of about 25–30 km along Wadi Nisah. Additionally, we used available gravity data to image the subsurface structure containing the aquifer. MT results indicated a low resistivity layer, associated with alluvium deposits, which was defined at a depth of about 1–2 km and extended horizontally about 15 km. Gravity data analysis was used to model this resistivity layer indicating a basement surface at 3–4 km depth.

Seismicity and major geologic structures of Tiran and Sanafir islands and their surroundings in the Red Sea

Tiran and Sanafir islands and their surrounding areas are very important due to their location within the Red Sea, which is in a triple junction among the African and Arabian plates and the Sinai Peninsula microplate. Consequently, this area should be studied from a geological point of view, particularly because there is a plan to construct King Salman’s bridge connecting Egypt and Saudi Arabia. Freely available potential field data, such as magnetic and gravity data, were integrated with seismological data from nearby seismic stations to understand the regional structure and seismic activity in the area. Potential field data were analysed using edge detection techniques (Tilt DeRivative and horizontal gradient) for qualitative interpretation and 2D inversion modelling for quantitative interpretation. Seismological data were analysed geostatistically to identify many epicentre locations and estimate the focal depths. The results of the potential field data analysis indicate that Tiran and Sanafir islands are located along a subsurface geological edge trending NW, parallel to the Red Sea. A similarity in potential field anomalies between both islands and the southern Sinai Peninsula indicates that these islands were separated from the Sinai Peninsula during the formation of the Gulf of Aqaba via Dead Sea Transform fault. The analysis of the seismic data indicates that a specific motion characterizes each focal depth solution. The seismic events are related to main structural trends NW–SE and NE–SW.