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New challenges in seismic mapping of the Earth's mantle: anisotropy, temperature, composition

English title New challenges in seismic mapping of the Earth's mantle: anisotropy, temperature, composition
Applicant Boschi Lapo
Number 134718
Funding scheme Project funding
Research institution Institut für Geophysik ETH Zürich
Institution of higher education ETH Zurich - ETHZ
Main discipline Geophysics
Start/End 01.11.2011 - 31.10.2013
Approved amount 114'598.00
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All Disciplines (3)

Discipline
Geophysics
Mineralogy
Geochemistry

Lay Summary (English)

Lead
Lay summary

For several decades now, seismologists have been converting seismic observations (i.e. recordings of ground oscillations all over the globe following earthquakes) into three-dimensional maps of the speed of seismic waves within our planet. These "tomographic maps" (similar, on a quite different scale, to medical X-ray) of the Earth are useful to understand the dynamics of the slow convective flow believed to cause plate tectonics, and more in general the origin and history of the planet. In the first approximation, local variations in seismic wavespeed have been interpreted as caused by proportional variations in temperature alone: areas where seismic waves are fast are likely to be cold, and vice-versa. Our project tries to do better than this simplistic approximation, taking into account the effect of possible variations in the chemical composition (rather than just the temperature) of rocks. This requires the combination of different competences: we must not only understand the physics of elastic wave propagation (seismology) and viscoelastic flow (geodynamics), but also be able to estimate the composition of rocks (geochemistry) and how it affects their mechanical properties (mineral physics). Another often neglected property of wavespeed is its anisotropy, that is to say, its dependence upon the direction of wave propagation. We shall improve existing techniques to map anisotropy via seismic tomography. We shall then apply recent findings in experimental mineral physics and geodynamic flow modeling to understand seismic images of anisotropy in terms of the Earth's temperature, composition, and present and past convective flow.

Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Mantle dynamics in the Mediterranean.
Faccenna Claudio, Becker Thorsten, Auer Ludwig, Billi A., Boschi Lapo, et al. (2014), Mantle dynamics in the Mediterranean., in Reviews of Geophysics, 52, 283.
Savani: A variable-resolution whole-mantle model of anisotropic shear-velocity variations based on multiple datasets.
Auer Ludwig, Boschi Lapo, Becker Thorsten, Nissen-Meyer Tarje, Giardini Domenico (2014), Savani: A variable-resolution whole-mantle model of anisotropic shear-velocity variations based on multiple datasets., in J. Geophys. Res., 119, 3006.

Collaboration

Group / person Country
Types of collaboration
University of Southern California United States of America (North America)
- in-depth/constructive exchanges on approaches, methods or results

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
EGU general assembly 2013 Poster Seismic structure of the deep mantle arising from thermal, chemical and phase variations in spherical convection simulations with self-consistent mineral physics. 01.04.2013 Vienna, Austria Tackley Paul; Auer Ludwig; Boschi Lapo; Giardini Domenico;
AGU fall meeting Poster Whole-mantle radial anisotropy from multi-mode surface-wave dispersion and body-wave traveltimes. 03.12.2012 San Francisco, United States of America Giardini Domenico; Boschi Lapo; Auer Ludwig; Nissen-Meyer Tarje;
Structure and Dynamics of the Earth’s Deep Mantle workshop Poster Whole-mantle radial anisotropy from multi-mode surface-wave dispersion and body-wave traveltimes. 13.11.2012 Paris, France Auer Ludwig; Boschi Lapo; Giardini Domenico; Nissen-Meyer Tarje;
3rd QUEST workshop Poster Whole-mantle radial anisotropy from multi-mode surface-wave dispersion and body-wave traveltimes. 20.05.2012 Tatranska Lomnica (Slovakia), Slovakia Boschi Lapo; Nissen-Meyer Tarje; Auer Ludwig; Giardini Domenico;


Associated projects

Number Title Start Funding scheme
149121 New challenges in mapping seismic waveforms into the Earth's mantle: anisotropy and mantle flow 01.11.2013 Project funding
141552 The Earth's lithosphere-asthenosphere boundary region: Seismic tomography, seismic receiver functions, anisotropy and flow 01.01.2012 International short research visits
143605 Seismology with GPS: Mapping the Earth’s interiors with geodetic observations 01.09.2013 Project funding

Abstract

We propose to utilize seismic and other geophysical observations to improve on current models of the anisotropy and the thermal and compositional heterogeneity of the Earth’s mantle. We will convert diverse, comprehensive and growing databases of seismic observations into three-dimensional maps of the mantle, and carefully interpret maps in terms of convective flow and/or compositional heterogeneity. This effort will be accompanied by the development of original software, to quantify the sensitivity of seismic data to anisotropic structure better than currently possible. We propose a Ph.D. project (student A) who will focus on the analysis and tomographic inversion of seismic data, and will interpret quantitavely his or her results in connection with geodynamics and mineral physics. This part of the project is described in sections 2.3.2, 2.3.4, 2.3.5 and 2.4.1 of this document. A second graduate student (student B), will work on the development of original software, to quantify the sensitivity of seismic data to anisotropic structure better than currently possible, as described in sections 2.3.3, 2.3.4 and 2.4.2. In a collaborative effort, the software developed by student B will be integrated with the tomography tools employed by student A.An important deliverable of our project will be a new three-dimensional model of both compressional (P) and shear (S) seismic velocities, and their anisotropy, throughout the mantle. Our model will be based on a wider database, and more advanced forward and inverse theory than its predecessors, and will be accordingly more robust. Although the main tools that we shall use are seismological, our work will be multidisciplinary. After using seismic tomography to identify anisotropic, three-dimensional maps of the entire mantle, we will apply results from mineral physics to interpret differences between P and S velocity in terms of rheology and composition, and variations in anisotropy in terms of lattice-, crystallographic-, or shape-preferred orientation. Once this step is made, it will be possible to make a connection between seismic results and geodynamic predictions, verify whether our new models explain surface observables like gravity, topography, and plate motions, and whether our maps of anisotropy are in agreement with the modeled pattern of convective flow. Combining competence in tomographic imaging, experimental mineral physics and dynamic modeling, will allow us to simultaneously tune seismic images and flow models, progressively identifying a single, integrated model of the Earth’s mantle.
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