ATTENUATION OF SURFACE-WAVES ACROSS THE ARABIAN PENINSULA

Amplitude spectra of fundamental-mode Rayleigh and Love waves are used to determine shear-wave Q (Q(beta)) models for the upper crust of the Arabian peninsula. The observed spectra are compared to theoretical spectra computed for earthquakes with known fault-plane solutions. Shear-wave Q in the upper crust can be obtained by trial-and-error modeling to fit the slope of the amplitude spectra at short periods (5-30 s), if the source time function is less than about 6 s and if the depth of the earthquake is known to within about 3 km. Shear-velocity Q values obtained in this way vary from about 60 along the margin of the Red Sea to 100-150 in the central part of the peninsula, to 65-80 in the eastern folded region. These values are unusually low for a stable region and suggest that observed anelasticity there is affected by tectonic and epeirogenic activity which has occurred over the past 30 m.y. The shear-wave Q models derived from surface waves at periods of 5-30 s closely predict reported values of Lg Q at 1 Hz; shear-wave Q, therefore, appears to be independent of frequency in this region at periods between about 1 and 30 s.