Optimized Moment Tensor Inversion in Effective Three-Dimensional Seismic Earth's Model

Date: 4/26/2019

Time: 06:00 PM

Room: Grand Ballroom

The robustness of moment tensor inversion for source characterization relies on the accuracy of the Earth's seismic model, and the method used to compute Green's tensor in it.

Many moment tensor inversions are based on Green's functions calculated with approximate methods, which reproduced a limited part of the seismic wavefield, and are built on 1-D models or ad hoc 2-D or 3-D averages.

3-D seismic models and full numerical Green's functions can now be derived thanks to the recent advances in high-performance computing and seismic techniques, but some issues remain: taking the crust into account, or imaging it, still is a difficult task; and if done, the necessary fine spatial discretization for numerical seismic wave propagation within this highly heterogeneous medium, leads to time-consuming simulations, even for long-period signals.

Eventual remedies mainly involves the use of an artificial crustal layer or so-called 'junk crust' (Fichtner & Igel 2008).

We have developed a non-linear, stochastic inversion procedure to generate 3-D models adapted to numerical simulation of the full seismic wavefield.

This probabilistic approach is based on the parametrization of models using an optimized basis of smooth functions constructed by principal component analysis of an effective reference model (using some filtering inherited from the homogenization theory).

It provides a reduced and optimized parameter space for the Bayesian inversion of an ensemble of 1-D seismic models. An appraisal step of the ensemble of models is added to regularize the 3-D model laterally.

Using CUB (Shapiro & Ritzwoller 2002) as a starting block, our procedure allows for the determination of a three-dimensional, effective, seismic Earth model, and of full 3-D Green's functions - procured at a relatively low numerical cost with spectral element's simulations.

As an illustration, we generate optimized 3-D models and associated full 3-D Green's functions to invert for moment tensors associated to several events, and compare the results to those obtained using a more classical procedure.

Presenting Author: Gael Burgos

Authors