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Finite-frequency sensitivity of body waves to anisotropy based upon adjoint methods

Sieminski, Anne and Liu, Qinya and Trampert, Jeannot and Tromp, Jeroen (2007) Finite-frequency sensitivity of body waves to anisotropy based upon adjoint methods. Geophysical Journal International, 171 (1). pp. 368-389. ISSN 0956-540X. https://resolver.caltech.edu/CaltechAUTHORS:SIEgji07

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Abstract

We investigate the sensitivity of finite-frequency body-wave observables to mantle anisotropy based upon kernels calculated by combining adjoint methods and spectral-element modelling of seismic wave propagation. Anisotropy is described by 21 density-normalized elastic parameters naturally involved in asymptotic wave propagation in weakly anisotropic media. In a 1-D reference model, body-wave sensitivity to anisotropy is characterized by ‘banana–doughnut’ kernels which exhibit large, path-dependent variations and even sign changes. P-wave travel-times appear much more sensitive to certain azimuthally anisotropic parameters than to the usual isotropic parameters, suggesting that isotropic P-wave tomography could be significantly biased by coherent anisotropic structures, such as slabs. Because of shear-wave splitting, the common cross-correlation travel-time anomaly is not an appropriate observable for S waves propagating in anisotropic media. We propose two new observables for shear waves. The first observable is a generalized cross-correlation travel-time anomaly, and the second a generalized ‘splitting intensity’. Like P waves, S waves analysed based upon these observables are generally sensitive to a large number of the 21 anisotropic parameters and show significant path-dependent variations. The specific path-geometry of SKS waves results in favourable properties for imaging based upon the splitting intensity, because it is sensitive to a smaller number of anisotropic parameters, and the region which is sampled is mainly limited to the upper mantle beneath the receiver.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1111/j.1365-246X.2007.03528.xDOIUNSPECIFIED
ORCID:
AuthorORCID
Tromp, Jeroen0000-0002-2742-8299
Additional Information:©2007 The Authors. Journal compilation © 2007 RAS. Accepted 2007 June 20. Received 2007 June 15; in original form 2007 March 19. We thank Sonja Greve, Martha Savage, an anonymous reviewer and editor Cindy Ebinger for helpful comments and suggestions. The adjoint spectral-element computations discussed in this paper were performed on Caltech's Division of Geological & Planetary Sciences Dell cluster. The source code for the adjoint spectral-element simulations is freely available from http://www.geodynamics.org. We gratefully acknowledge support from the European Commission's Human Resources and Mobility Programme, Marie Curie Research Training Networks, FP6 and by the National Science Foundation under grant EAR-0309576. This is contribution no 9170 of the Division of Geological & Planetary Sciences of the California Institute of Technology.
Subject Keywords:adjoint methods, bodywaves, Frechet derivatives, seismic anisotropy, sensitivity, shear-wave splitting
Issue or Number:1
Record Number:CaltechAUTHORS:SIEgji07
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:SIEgji07
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:9583
Collection:CaltechAUTHORS
Deposited By: Lindsay Cleary
Deposited On:11 Feb 2008
Last Modified:09 Mar 2020 13:19

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