Date of Award

6-1994

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Mohammed Mamdouh Khattab

Second Advisor

Mohammed Fathy Hamoda

Third Advisor

Dr.Mohammed Ubaid Qubati

Abstract

An interpretive geophysical study in the growing Salalah Plain, Dhofar Governate, Sultanate of Oman, was made during 1993 and part of 1994.

This investigation stems from the need to develop the main and the only water resource in this region. It is aimed to make use of the combined geophysical tools (seismic rflection, gravity, magnetics and resistivity) and available surface and borehole data to assess the environmental impact of the geophysical results.

Several seismic reflection lines were picked and interpreted; one on a horizon near the Taqah limestone (main aquifer), and the other on a horizon near the Mesozoic- Cenozoic boundary.

Using appropriate algorithms, the 0.5 mGal Bouguer anomaly gravity map, and the 10 nT (gamma) total magnetic intesity maps of the Salalah Plain were processed. A least-sequares polynomial fitting program was used to remove the intensive gravity regional. A subsurface geologic model based on observed gravity and magnetic data was calculated down to the continental basement.

Several gravity and magnetic profiles were constructed to evaluate the sedimentological and structural setup of the near surface section. The surface and borehole resistivity measurements were jointly interpreted with seismic, gravity, magnetic and borehole data.

The time map at the Salalah aquifer confirmed the elongate trough already producing potable water and revealed an additional trough, in the eastern Salalah Plain (south of Wadi Sahalnout) of prospective ground water reservoir. In addition, the time maps on both shallow and deep levels showed few normal faults affecting the aquifer.

Gravity and magnetic maps showed a major basement depression of E-W axis with gradients probably related to normal faulting associated with the epoch of Gulf of Aden extension during the Modelling of gravity and Oligocene and Miocene magnetic data indicate a heterogenous continental basement ovelain by more than 5.0 km of Mesozoic, Cenozoic and younger alluvial sediments.

A residual gravity map suggests a shallow and significant upwarp near the main aquifer. Magnetic profiles showed shallow igneous bodies. Both seismic and potential field data suggest the existence of normal faulting which is significant in controlling the subsurface flow of ground water from wasting into the Arabian Sea.

The seismic-inferred axis of the main aquifer, in the Salalah Plain, is known to posses sampled minimum salinity. The flanks of the delineated seismic trough roughly mark the brackish-potable water boundary. Single point borehole resistivity measurements are found to correlate inversely with seismic-inferred depth to the aquifer In that the highest resistivity values lie near the axis of the depression. This should add importance to the easterly-located seismic trough.

The delineation of additional depression and the indication of structural control of this important area through the collective interpretation of seismic, potential field, and borehole data should add momentum in the development of the growing Salalah Plain. The addition (through this investigation) of prospective new acreage in the eastern part of the Salalah Plain to the already existing land use map is significant.

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