Abstract
Based on a two-dimensional ray path interpretation of travel time and wave amplitude ratios, a detailed crustal velocity structure of central Saudi Arabia has been derived using the deep-seismic refraction profile of Saudi Arabia. The crustal model derived significantly differs from previous interpretations carried out on the same data set since more energetic crustal phases were considered in this analysis. The two-dimensional crustal model derived shows that the crust consists of four distinct layers. It is approximately 42 km thick under the Arabian platform and thins gradually in a southwest direction to about 38 km under the shield. The upper crust consists of two layers. The first one has a P-wave velocity of about 6.1 km/s, and is about 3 km thick thinning to about 1 km under the platform. The second layer has a P-wave velocity of about 6.2 km/s and is about 14 km thick but thins to about 7 km under the platform. The intermediate crustal layer has a P-wave velocity of about 6.4 km/s, is about 7.5 km thick under the shield; under the platform it is about 16 km thick with a velocity of about 6.3 km/s. The lower crust has a P-wave velocity of about 6.9 km/s and is about 15 km thick. A decrease in the upper mantle Pn velocity from 8.2 to 8.1 km/s seems to accompany the crustal thinning. The Moho discontinuity is sharply defined beneath the shield and gently dips towards the northeast. A significant crustal inhomogeneity in the region separating the Afif terrane from the Ar Rayn terrane is interpreted as a thrusting system, rather than a distinct vertical discontinuity in the crustal structure, as previously interpreted. This region between the two terranes, which is of different crustal composition, is probably the result of thrusting and emplacement of nappes of upper crustal materials of the Afif terrane onto the Ar Rayn foreland. The nature and location of this zone were constrained by travel time and wave amplitude ratio measurements. The detailed velocity crustal model derived in this study is of significant importance in earthquake studies, tectonics, and determining the evolution of the Arabian Plate.
Published Version
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