1ST EVIDENCE FOR HIGH ANELASTIC ATTENUATION BENEATH THE RED-SEA FROM LOVE WAVE ANALYSIS

Attenuation coefficients of Love waves are determined for two seismic paths along the Red sea. The attenuation coefficients are obtained using the multiple filter method for periods from 25 to 130 s along one path and from 40 to 130 s along the second one. The two sets of observations are in good agreement with anomalously high attenuation coefficients similar to those reported across a young part of the Pacific ocean. Indeed, the values lie on average between 3.3 ± 0.6 and 1.1 ± 0.3(10−4km−1), higher values being observed at shorter periods. In a second part of the paper, these apparent attenution observations are interpreted in terms of a distribution of intrinsic absorption in the upper mantle. A frequency independent Qβ model is obtained using a trial‐and‐error method. The best fit to the data required a large and very low Qβ (30–50) zone below a depth of 50 km, underlying a thin and high Qβ (200–300) lid. These results are consistent with high heat flows and low velocities which characterize this tectonically active area, and corroborate the inference of anomalously high temperatures and low viscosity in the upper mantle beneath the Red Sea from recent seismological results. Copyright 1990 by the American Geophysical Union.