Velocity dispersion and amplitude attenuation of Rayleigh waves across thePhilippine Sea

The fundamental-mode interstation group and phase velocities and attenuatio n coefficients of Rayleigh waves along four paths across the Philippine Sea are determined to have periods of between 20 and 110 seconds by the two-st ation method. The values of group and phase velocities are quite consistent with the results of previous studies using the single-station method. Grou p and phase velocities vary significantly with different wavepaths at perio ds of less than 50 seconds, but for longer periods, the phase velocities ar e quite close. The inversion results show that the thickness of the lithosp here is about 60 km in the Philippine Sea, except in the area of the easter n volcanic islands where a slightly thinner lithosphere (about 50 km) is de duced, The attenuation coefficients observed in the Philippine Sea are high er than the values obtained in the Pacific. This result simply reflects tha t the Philippine Sea plate is younger than that of the Pacific. Lateral. va riation in attenuation coefficient is not as clear as it is in velocity bec ause of its large variance. However, the vertical distribution of Q(beta)(- 1) is quite similar to that for the shear velocity model.