Crustal structure of the Northwestern part of the Arabian Shield in Saudi Arabia deduced from gravity data

Abstract

The present-day tectonics of the Northwestern Region of Saudi Arabia is affected by the tectonics related to the Red Sea floor spreading. The tectonic movemets related to the Red Sea floor spreading creat great variations in the crustal structure and depth of Moho discontinuity through this region. Gravity data have been acquired from Earth Gravitional Model (EGM-2008) and analyzed to estimate the crustal thickness under this region. 2-D gravity modeling have been conducted along eleven profiles oriented ENE-WSW and NW-SE to verify the lateral variations of the crust and mantle beneath these profiles. Accordingly, the upper layer of the crust is represented by sedimentary rocks underlying by basement layer that extends until the Moho discontinuity. The crustal thickness increases eastward,and the depth to the Moho is 25 km in the western part, along the Red Sea and increased upto 38 km through the Arabian Shield. These results are in agreement with the previous deep seismic and seismological investigations. The relation between recent earthquake swarms at Harrat Al-Shaqah area and the variations of Moho depth through the Northwestern Region has been clarified. It can be concluded that, these earthquake activities are of crustal origin and occurred due to the stresses exerted upon the pre-existed faults by mantle upwelling in this region. These results can be confirmed by the presence of the recent volcanic activities that experienced the Western Region of Saudi Arabia. Key words: Western Region of Saudi Arabia, Red Sea, tectonics, Arabian Shield.