Seismic attenuation in the Middle America Region and the frequency dependence of intrinsicQ

Abstract

We evaluate the mechanisms of attenuation for the Middle America (MA) region in the range of 1.0≤f≤15 Hz. Our analysis focuses on reconciling laboratory experiments, which suggest that in this frequency range, intrinsic attenuation has a weak to zero frequency dependence, with results obtained using the Multiple Lapse Time Widow (MLTW) method. The MLTW method is designed to separate the contributions of scattering by heterogeneities and intrinsic attenuation from total attenuation assuming spherical geometrical spreading and isotropic scattering. Application of the MLTW method suggests that total attenuation in the MA region is concentrated towards the upper crust and is relatively constant throughout the region. It also shows a strong frequency dependence of the energy loss component of the attenuation (apparent intrinsic attenuation). We test the effect that forward and back scattering operators, distribution of the sources, and absorption of energy into the mantle has on the separation of the components of attenuation. We conclude that the inclusion of the frequency‐dependent leakage of energy towards the mantle provides a mechanism to satisfy both laboratory experiments and estimates based on the MLTW method. For the Middle America region, we find that the intrinsic attenuation.