The Anelastic Attenuation of Surface Waves Beneath Southwestern Arabia and the Southern Red Sea

The seismic attenuation coefficients of surface waves in southwestern Arabian Peninsula and the southern Red Sea were inves- tigated using the station ratio method. Love and Rayleigh waves data recorded by two GSN stations RAYN and ATD are used to compute Love and Rayleigh waves attenuation coefficients (γ L and γ R ), and Love and Rayleigh waves internal friction (Quality factors, Q L and Q R ) in the region between the two GSN seismic stations RAYN and ATD. RAYN lies at the center of Arabia, while ATD is located on the western coast of the southern Red Sea on the Afar depression. γ R is found to vary from a low of 4.03 × 10 -4 km -1 at 27 s and a high of 22.9 × 10 -4 km -1 at 44 s. γ L , on the other hand, varies between a mini- mum of -2.28 × 10 -4 km -1 at 6 s and a maximum of 10.81 × 10 -4 km -1 at 23 s. The average quality factors Q R and Q L for the upper crust are estimated to be 100 and 160, respectively. Surface wave attenuation below the upper crust is extremely high. The high attenua- tion of the crust and upper mantle may be explained in the frame work of the ongoing tectonic process of the Red Sea and the Afar depres- sion. High temperature associated with partial melting beneath the crust can result in increasing the attenuation which is observed at long periods, while at short periods (less than 27 s), the level of attenuation is less. However, the attenuation is remarkably high. The results of this confirm previous indications that the Arabian plate, unlike other stable regions, has unusually higher attenuation characteristics for seismic waves in the crust and upper mantle comparable to many tectonically active regions of the world.