SINISTRAL MOVEMENT ALONG THE MARADI FAULT, OMAN: EVIDENCE FROM SIR-C RADAR DATA

Evidence from Spaceborne Imaging Radar (SIR-C) data shows that the Maradi fault, in the NE part of the Arabian Peninsula, (centered around 22 degs 15'N, 58 degs E), has a component of sinistral strike-slip displacement and not dextral as commonly supposed.

The Maradi fault is a major NW-striking fault in the NE part of the Arabian Peninsula in northern Oman, traceable for at least 60 km. It merges with a foreland fold-belt to the NW, and disappears beneath a Quaternary alluvial plain to the SE, but may re-emerge as the Saiwan-Nafun fault in the Huqf area of central Oman. The fault forms a N-facing escarpment defined by the Lower Hadhramaut Group shelf facies (Fiqa Formation), with a reduced elevation of about 20 m on its NE side. The gently undulating topography, and a heavy clay signature obscuring the fault, makes identification difficult in Thematic Mapper (TM) images. Radar images, on the other hand, illustrate its continuity.

Recognition of tectonic features in radar images depends on viewing geometry and incidence angle. In this study, the images were collected in descending (left-looking) orbit at incidence angles between 36 degs and 43.7 degs. The relatively high angles enhance surface roughness effects and minimize slope effects - the necessary configuration for the identification of this regionally extensive fault. Sub-surface imaging also occurs at these localities owing to the semi-arid climate in Oman (thus, dry conditions), fine-grained cover material, and gently undulating terrain.

Two features indicate that the fault has a component of sinistral motion. First, a large, pre-Miocene, unnamed drainage channel is displaced in a left-lateral direction. The channel does not correspond to any mapped drainage, nor is it visible in TM imagery; hence, it must be sub-surface, beneath the Tertiary Barzaman formation. Second, the Tertiary, ferrugnized and karstified palaeosurface of the Upper Fars Group is displaced to the left, again supporting sinistral strike-slip movement of the fault. Thus, it is deduced that sinistral strike-slip displacements were active along the Maradi fault throughout the Tertiary period.