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Towards Improved Understanding of Seismic Moment Tensors: Utilizing High-Resolution Earth Model with Accompanying Uncertainty Within Hierarchical Bayesian Inversion Framework


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The relative significance of the isotropic component in a moment tensor (MT) solution is critical in discriminating explosive events. For critically shallow sources, such as manmade explosions, it is challenging to resolve the isotropic (ISO) from vertical compensated linear vertical dipole (CLVD) components, because the focal mechanisms generate highly similar waveforms at regional distances. Additionally, rigorous quantification of uncertainty of data noise, mainly due to the observational process, and theoretical error, primarily due to imperfect knowledge of Earth structure, remains at the forefront of MT inversion research. Here, we attempt to progress on these research fronts. First we investigate an inversion scheme where data noise and structural uncertainty, empirically estimated for 1D Earth models, are constructed into covariance matrices defining the likelihood function (Phm and Tkalcic, 2021). Second, we explore the use of the affine-invariant ensemble samplers, which prove efficient in exploring the mechanism trade-off for shallow source depths. Also in this attempt, to account for Earths model uncertainty, we treat the time shifts between observed and synthetic waveforms as a proxy for heterogeneity of the Earth along propagation paths. Third, we explore a representation of 3D earth structure uncertainty in the form of empirical covariance matrices. In all cases, we demonstrate the importance of properly treating Earth's structure uncertainty in MT inversion, but the intrinsic trade-off in shallow seismic sources remains to be further investigated.



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