Azimuthal anisotropy of Lg attenuation: both real and synthetic data
Abstract
We typically expect the intrinsic attenuation of shear wave energy to be isotropic, scattering attenuation likely should be highly anisotropic. We observed strong azimuthal anisotropy of effective L g Q both in the eastern Tibetan Plateau and the northern Middle East. The direction of least attenuation generally correlates with the orientation of major geological structures, such as large strike-slip faults. In order to better understand the origin of anisotropic effective Q, we conducted several models with the open source code package SW4 with different velocity and intrinsic shear wave attenuation structures. The models are with dimension 1000 km (L) × 1000 km (W) × 400 km (H). It takes about 6 hours on 300 processors for each model for one source and we run 8 sources uniformly distributed near the boundaries for each model to get full azimuthal coverage. Then we manually picked and applied reverse two-station method (RSM) to the synthetic waveforms to get effective L g Q along each path and sparse equation and least squares (LSQR) method to generate an anisotropic L g Q model. The advantage of RSM is to get rid of both source and site effect, so that the anisotropy only comes from path.
As we see in the real data, we observed azimuthal anisotropy of effective L g Q along the boundaries of velocity anomalies, even with constant intrinsic shear attenuation. This phenomena may be the result of that scattering attenuation is highly directionally dependent within anisotropic medium. This results help us better understand the effect of scattering attenuation and its relation to the velocity anomalies within crust.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.S41F0591H
- Keywords:
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- 0545 Modeling;
- COMPUTATIONAL GEOPHYSICS;
- 7260 Theory;
- SEISMOLOGY;
- 7270 Tomography;
- SEISMOLOGY;
- 7290 Computational seismology;
- SEISMOLOGY