Determining Q of near-surface materials from Rayleigh waves

High-frequency (greater than or equal to2Hz) Rayleigh wave phase velocities can be inverted to shear (S)-wave velocities for a layered earth model up to 30 in below the ground surface in many settings. Given S-wave velocity (V-S), compressional (p)-wave velocity (V-P), and Rayleigh wave phase velocities, it is feasible to solve for P-wave quality factor Q(P) and S-wave quality factor Q(S) in a layered earth model by inverting Rayleigh wave attenuation coefficients. Model results demonstrate the plausibility of inverting Q(S) from Rayleigh wave attenuation coefficients. Contributions to the Rayleigh wave attenuation coefficients from Q(P) cannot be ignored when Vs/V-P reaches 0.45, which is not uncommon in near-surface settings. It is possible to invert Q(P) from Rayleigh wave attenuation coefficients in some geological setting, a concept that differs from the common perception that Rayleigh wave attenuation coefficients are always far less sensitive to Q(P) than to Q(S). Sixty-channel surface wave data were acquired in an Arizona desert. For a 10-layer model with a thickness of over 20 in, the data were first inverted to obtain S-wave velocities by the multichannel analysis of surface waves (MASW) method and then quality factors were determined by inverting attenuation coefficients. (C) 2002 Elsevier Science B.V. All rights reserved.