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Imaging subsalt is still a challenging task in oil gas exploration. We utilized magnetotellurics to improve the integration of seismic and gravity data to image the Wedehof salt dome, Northern Germany. High-resolution natural field source broadband magnetotelluric (MT) data were acquired and enhanced the definition of the top and overhanging salt structures in addition to the description of the salt dome root. Salt boundaries show strong resistivity contrasts with the surrounding sediments and thus represent a good target for electromagnetic measurements, especially for mapping the top salt horizon. Using broadband array data acquisition and advanced processing techniques, difficulties with cultural noise sources could be solved. With integrated 3D gravity modeling focusing on the salt dome's flanks at intermediate depths an improved model could be achieved. The revised salt geometries provided sound input to a seismic reprocessing and led to an improved imaging of the subsalt areas proven by subsequent exploration drilling. The integrated interpretation of magnetotellurics, gravity and seismics combines the strengths of the different physics, thus increasing the imaging reliability and reducing exploration drilling risks. In this case, we used a conservative workflow that includes a survey feasibility study with field noise evaluation and careful acquisition parameter testing at the beginning of the survey. Only with this we could overcome the cultural noise issues associated with the survey area being near large cities and their associated electromagnetic noise.

The Authors have deduced from seismic, gravity and other geophysical data that strike‐slip processes mainly controlled the early break‐up stages of the Arabian Plate from Africa, initiating the Red Sea Rift. Sea‐floor spreading is only 5 million yrs old, and is still limited in the central and parts of the southern Red Sea. The area was a zone of structural weakness as early as 600 million yrs ago, and was reactivated in the late Oligocene with intense magmatic activity and the development of a continental rift. Wrench‐faulting shaped most of its western flank as a sharp plate boundary, while the eastern flank is floored by stretched continental crust due to uplifting and shifting of Arabia from Africa. Wrench‐faulting was controlled by pre‐existing fault systems, such as the Najd Shear System, the Central African Fault Zone, or the Onib‐Hamisana and Baraka sutures. As a consequence, both wrench‐faulted transtensional and transpressional areas developed. Transtensional basins are evident offshore Egypt, the Sudan and the Gulf of Aqaba; while the island of Zabargad is a remnant transpressional area. With Arabia as the “mobile” plate and Africa relatively “stable”, the eastern Red Sea flank was formed through stretching, thinning and diffuse extension, and is floored by attenuated continental crust, thus producing the asymmetry observed in seismic sections between the eastern and western flanks of the Red Sea Rift. The Dead Sea strike‐slip fault only experienced intense deformation during the last 14 million yrs. Plate motion was oblique to the initial orientation of the basin, and could no longer be accommodated by the opening of the Gulf of Suez; the en échelon distribution of gravity and magnetic anomalies as well as the high heat‐flow fields recorded in the northern Red Sea are Gulf of Aqaba oriented due to this process. Similarly, the thinned continental crust between Yemen and Ethiopia is affected by shear‐faults that displace the volcanic centres to the east. The bathymetry reflects the tectonic processes described above, and the mineralisation in the metalliferous “deeps” is tied either to Recent sea‐floor spreading centres or to the en‐échelon distributed fractures along the Red Sea flanks. Sedimentary basins, aligned along the stretched continental, flanks of the Red Sea, are important for oil and gas exploration.

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