Measurements of translation, rotation and strain: new approaches to seismic processing and inversion
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We propose a novel approach to seismic tomography based on the joint processing of translation, strain and rotation measurements. Our concept is based on the apparent S and P velocities, defined as the ratios of displacement velocity and rotation amplitude, and displacement velocity and divergence amplitude, respectively. To assess the capability of these new observables to constrain various aspects of 3D Earth structure, we study their corresponding finite-frequency kernels, computed with a combination of spectral-element simulations and adjoint techniques. The principal conclusion is that both the apparent S and P velocities are generally sensitive only to small-scale near-receiver structure, irrespective of the type of seismic wave considered. It follows that knowledge of deeper Earth structure would not be required in tomographic inversions for local structure based on the new observables. In a synthetic finite-perturbation test, we confirm the ability of the apparent S and P velocities to directly detect both the location and the sign of shallow lateral velocity variations.
KeywordsEarth structure Earthquakes Geophysical techniques Seismic waves Seismology
We thank the members of the Munich Seismology group (LMU University, Munich) for the many critical and fruitful discussions. The research presented in this article was supported by the International Graduate School THESIS within the Bavarian Elite Network. Andreas Fichtner was funded by The Netherlands Research Center for Integrated Solid Earth Sciences under project number ISES-MD.5. The numerical computations were performed on the National Supercomputer HLRB-II maintained by the Leibniz-Rechenzentrum. The constructive criticism of two anonymous reviewers allowed us to improve the first version of our manuscript.
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