THORSTEN W. BECKER
Department of Earth Sciences
University of Southern California
Los Angeles

Geodynamics research
[news] [research] [publications] [group] [CV] [teaching] [downloads] [contact] [misc]
[geodynamics] [seismology] [SEATREE] [downloads] [lab]
[anisotropy] [global mantle dynamics] [subduction] [western US]

  • Seismic anisotropy and the asthenosphere

    • Radial anisotropy as a constraint for rheology

      We present the first global forward model of radial anisotropy and are able to match both anisotropy averages and some of the anomaly patterns. The mismatch between seismology and geodynamic reference, residual anisotropy, yields information on the frozen-in structure of the tectosphere and the volatile content and dynamics of the asthenosphere. An NSF-Geophysics funded project.
      • Becker, T. W., Kustowski, B. and Ekström, G.: Radial seismic anisotropy as a constraint for upper mantle rheology. Earth Planet. Sci. Lett., 267, 213-237, 2008. (PDF)

    • Azimuthal anisotropy from surface waves and flow models

      We show that anisotropy constrains net rotations of the lithosphere to be smaller than in some hotspot reference frame models, and analyze different seismological models using generalized spherical harmonics. Geodynamics can provide an both heterogeneity power spectra and patterns. An NSF-Geophysics funded project.
      • Becker, T. W.: Azimuthal seismic anisotropy constrains net rotation of the lithosphere. Geophys. Res. Lett., 35, L05303, doi:10.1029/2007GL032928, 2008. (Correction: 2008GL033946, PDF)
      • Becker, T. W., Ekström, G., Boschi, L., and Woodhouse, J.: Length scales, patterns, and origin of azimuthal seismic anisotropy in the upper mantle as mapped by Rayleigh waves. Geophysical J. Int., 171 451-462, 2007. (PDF)

    • Length scales and origin of continental anisotropy

      We analyze the lateral variations in anisotropic length scales as inferred from SKS splitting. Older continental regions appear more coherent than younger, geologically active units. We interpret this finding using surface waves and geodynamic models; anisotropy in old cratons may reflect frozen-in structure in the thick tectosphere rather than asthenospheric flow as underneath oceanic plates.

      • Becker, T. W., Browaeys, J. T., and Jordan, T. H.: Stochastic Analysis of Shear Wave Splitting Length Scales. In press at Earth and Planetary Science Letters, 259, 526-540, 2007. (PDF)

    • LPO texturing, mantle flow, and xenolith fabrics

      We study upper mantle fabrics from different mineral physics texturing models and mantle convection simulations with lateral viscosity variations. Texturing methods are found to differ strongly in terms of the treatment of recrystallization and predictions of mechanical anisotropy. Flow modeling results indicate that scaling relationships exist between hexagonal anisotropy parameters, and that natural samples follow the same trends as synthetics. Previously NSF-CSEDI funded.

      • Castelnau, O., Blackman, D. K. and Becker, T. W.: Numerical simulations of texture development and associated rheological anisotropy in regions of complex mantle flow. Geophys. Res. Lett, 36, L12304, doi:10.1029/2009GL038027, 2009. (PDF)
      • Becker, T. W., Chevrot, S., Schulte-Pelkum, V., and Blackman, D. K.: Statistical properties of seismic anisotropy predicted by upper mantle geodynamic models. J. Geophys. Res., 111, B08309, doi:10.1029/2005JB004095, 2006. (PDF).

    • Regional flow underneath the western United States

      We study regional shear wave splitting observations for the western United States and interpret them in a comprehensive modeling framework. We find evidence for a deep counterflow underneath North America driving by the Farallon slab. An NSF-CSEDI funded project.

      • Becker, T. W., Schulte-Pelkum, V., Blackman, D. K., Kellogg, J. B., and O'Connell, R. J.: Mantle flow under the western United States from shear wave splitting, Earth and Planetary Science Letters, 247, 235-251, 2006. (PDF)

    • Global upper mantle deformation and azimuthal anisotropy

      We compare finite strain from flow-models with Rayleigh-wave observations of azimuthal seismic anisotropy. Finite strain is a better explanation for anisotropy orientations than alignment with absolute plate motions, and we find evidence for buyoancy driven upwellings.

      • Becker, T. W., Kellogg, J. B., Ekström, G., and O'Connell, R. J.: Comparison of azimuthal seismic anisotropy from surface waves and finite-strain from global mantle-circulation models, Geophysical Journal International, 155, 696-714, 2003. (PDF)

  • Global mantle dynamics

    • Generation of plate tectonics and mantle heterogeneity from convection

      We use spherical convection models in 3-D to study which rheological parameters lead to plate-tectonics like surface motions and are able to match tomographically inferred heterogeneity spectra self-consistently.

      • Foley, B. and Becker, T. W.: Generation of plate-like behavior and mantle heterogeneity from a spherical, visco-plastic convection model. Geochem., Geophys., Geosys., 10, Q08001, doi:10.1029/2009GC002378, 2009. (PDF)

        Top weekly download spot at G-Cubed and picked as highlighted image in August 2009 (G-Cubed "cover" from 08/2009).

    • Variability in Cenozoic heatflow and thermal history

      We use reconstructions of seafloor age and plate geometry variations over the Cenozoic to infer the character of mantle heat transport and plate tectonic cyclicity.

      • Becker, T. W., Conrad, C. P., Buffett, B. and Müller, R. D.: Past and present seafloor age distributions and the temporal evolution of plate tectonic heat transport. Earth Planet. Sci. Lett., 278, , 233-242, 2009. (PDF)
      • Loyd, S. J., Becker, T. W., Conrad, C. P., Lithgow-Bertelloni, C., and Corsetti, F.A.: Time-variability in Cenozoic reconstructions of mantle heat flow: plate tectonic cycles and implications for Earth's thermal evolution Proceed. Nat. Acad. Sci., 104, 14266-14271, 2007. (PDF)
        • Popular science coverage: UPI (picked up by EarthTimes, Science Daily, First Science, Eureka Alert, PhysOrg, Terra Daily, NewsWise, Geology Times etc.), USC, USC College

    • Plume detection

      We analyze geodynamic and seismological models of the mantle and demonstrate that tomography images deep mantle plumes that connect to surface hotspots if conduit distortion in the mantle wind is accounted for.

      • Boschi, L., Becker, T. W., and Steinberger, B.: On the statistical significance of correlations between synthetic mantle plumes and tomographic models. Physics Earth Planet. Int., 260, 230-238, 2008. (PDF)
      • Boschi, L., T. W. Becker, and B. Steinberger, Mantle plumes: Dynamic models and seismic images, Geochem. Geophys. Geosyst., 8, Q10006, doi:10.1029/2007GC001733, 2007. (PDF)

    • Plate velocities, the geoid, mantle tractions and lithospheric deformation

      We have several ongoing collaborative efforts to refine our understanding of global and regional mantle circulation, what tractions might be expected to be transmitted to the lithosphere, why the plates move the way they do, and which geological processes might be associated with a deep origin.

      • Ghosh, A., Becker, T. W., and Zhong, S.: Effects of lateral viscosity variations on the geoid. Submitted to Geophys. Res. Lett., 2009. (PDF).
      • Bullen, A. L., McNamara, A., Becker, T. W., and Ritsema, J.: Global scale models of the mantle flow field predicted by synthetic tomography models. Submitted to Phys. Earth Planet. Int., 2009. (PDF)
      • Kaus, B, Liu, Y., Becker, T. W., Yuen, D., and Shi, Y.: Lithospheric stress-states predicted from long-term tectonic models: influence of rheology and possible application to Taiwan. J. Asian Earth Sci., 36, 119-134, 2009. (PDF)
      • Faccenna, C., Rossetti, F., Becker, T. W., Danesi, S., and Morelli, A: Recent extension driven by mantle upwelling at craton edge beneath the Admirality Mountains (Ross Sea, East Antarctica). Tectonics, 27, TC4015, doi:10.1029/2007TC002197, 2008. (PDF)
      • Becker, T. W.: On the effect of temperature and strain-rate dependent viscosity on global mantle flow, net rotation, and plate-driving forces. Geophys. J. Int., 167, 943-957, 2006. (PDF)
      • Becker, T. W. and O'Connell, R. J.: Predicting plate motions with mantle circulation models, Geochemistry, Geophysics, Geosystems, 2(12), doi:10.1029/2001GC000171, 2001. (PDF)
      • Becker, T. W. and O'Connell, R. J.: Lithospheric stresses caused by mantle convection: the role of plate rheology (abstract)EOS Trans. AGU, 82, F, 2001. (PDF)

    • Thermal constraints on the survival of primitive blobs in the lower mantle

      We examine mantle blobs, a mantle convection model that could reconcile geochemical data with geophysical evidence for whole mantle convection. Our analytical model shows that stiff blobs could serve as a geochemical reservoir over geologically long timescales even if they were to heat up by means of enrichment in heat producing elements.

      • Becker, T. W., Kellogg, J. B., and O'Connell, R. J.: Thermal constraints on the survival of primitive blobs in the lower mantle. Earth Planet. Sci. Lett., 171, 351, 1999. (PDF)

    • A comparison of seismologic and geodynamic mantle models

      We present a comprehensive and quantitative comparison between recent seismological and geodynamic models of the Earth's mantle to help in the move from mapping to hypotheses testing. Our results are compatible with whole mantle convection with reorganization of flow at 660-km due to the viscosity jump.

      • Becker, T. W. and Boschi, L.: A comparison of tomographic and geodynamic mantle models, Geochemistry, Geophysics, Geosystems, 3(1), 1003, doi:10.1029/2001GC000168, 2002. (PDF)

      You can find the additional online material and tomographic model expansions on the Becker & Boschi: Correlations between models page. All tomographic models from that repository can be used directly as input for hc, for example in the Solid Earth Research and Teaching Environment (SEATREE) GUI.

      • Milner, K., Becker, T. W., Boschi, L., Sain, J., Schorlemmer, D. and H. Waterhouse: The Solid Earth Research and Teaching Environment: a new software framework to share research tools in the classroom and across disciplines. Eos Trans. AGU, 90, 12, 2009. (PDF).
      • Waterhouse, H. D., K. Milner, T. W. Becker, J. Sain, and D. Schorlemmer: A Solid Earth Research and Teaching Environment, Opportunities and Challenges in Computational Geophysics workshop, Caltech, 2009. (PDF).

    • Global semi-analytical flow code benchmark

      Supported by CIG's Mantle Convection working group, I am coordinating a benchmark and recoding effort to establish a shared, modular and flexible implementation of a Hager & O'Connell (1981) type program for solving for velocities in the viscous mantle. Download instructions for the code are found here (under: hc). You can download the work plan with summary of results as PDF here; please send me an email if you would like to participate in this effort.

      As a product of this effort, a simple, modular, C-language implementation, hc, is available. HC is a module within the Solid Earth Research and Teaching (SEATREE) environment.

  • Subduction dynamics

    • Effect of elasticity on mantle convection

      We investigate the role of visco-elasticity for the formation of Rayleigh-Taylor type instabilities and lithospheric detachments.

      • Kaus, B. J. P. and Becker, T. W.: Effects of elasticity on the Rayleigh-Taylor instability: implications for large-scale geodynamics. Geophys. J. Int., 168, 843-862, 2007. (PDF)

    • Slab rollback and interaction with the 660

      We explore how regional subduction dynamics and viscosity stratification in the mantle can affect slab morphologies and plate velocities.

      • Becker, T. W. and Faccenna, C.: A review of the role of subduction dynamics for regional and global plate motions. In: Subduction Zone Geodynamics, Lallemand, S. and Funiciello, F. (eds), Int. J. Earth Sci., 3-34, 2009. (PDF)
      • Funiciello, F., Faccenna, C., Heuret, A., Di Giuseppe, E., Lallemand, S., and Becker, T. W.: Trench migration, net rotation and slab-mantle coupling. In press at Earth Planet. Sci. Lett., 271, 233-240, 2008. (PDF)
      • Kaus B. J. P., Becker T. W.. A numerical study on the effects of surface boundary conditions and rheology on slab dynamics. Bolletino di Geofisica, 49(2), p. 177-182, 2008. (PDF)
      • Faccenna, C., Heuret, A., Funiciello, F., Lallemand, S., and Becker, T. W.: Predicting trench and plate motion from the dynamics of a strong slab. Earth Planet. Sci. Lett., 257, 29-36, 2007. (PDF)
      • Piromallo, C., Becker, T. W., Funiciello, F., and Faccenna, C.: Three-dimensional instantaneous mantle flow induced by subduction, Geophys. Res. Lett., 33, L08304, doi:10.1029/2005GL025390, 2006. (PDF)
      • Enns, A., Becker, T. W., and Schmeling, H.: The dynamics of subduction and trench migration for viscosity stratification. Geophys. J. Int., 160, 761-775, 2005. (PDF)

    • The development of slabs in the upper mantle

      We study subduction in the upper mantle using a joint laboratory and numerical model approach, focusing on rollback and back-arc extension in the Mediterranean, and continental collision in Taiwan.

      • Becker, T. W. and Faccenna, C.: A review of the role of subduction dynamics for regional and global plate motions. In: Subduction Zone Geodynamics, Lallemand, S. and Funiciello, F. (eds), Int. J. Earth Sci., 3-34, 2009. (PDF)
      • Kaus, B, Liu, Y., Becker, T. W., Yuen, D., and Shi, Y.: Lithospheric stress-states predicted from long-term tectonic models: influence of rheology and possible application to Taiwan. J. Asian Earth Sci., 36, 119-134, 2009. (PDF)
      • Kaus, B. J. P., Steedman, C., and Becker, T. W.: From passive continental margin to mountain belt: insights from analytical and numerical models and application to Taiwan. Physics Earth Planet. Int., 171, 25-251, 2008. (PDF)
      • Faccenna, C., Becker, T. W., Lucente, F. P., Jolivet, L. and Rossetti, F.: History of Subduction and Back-arc Extension in the Central Mediterranean. Geophysical Journal International, 145, 809, 2001. (PDF)
      • Becker, T. W., Faccenna, C., O'Connell, R. J., and Giardini, D.: The development of slabs in the upper mantle: insights from experimental and laboratory experiments. Journal of Geophysical Research, 104, 15207, 1999. (PDF)

  • Dynamics of the western United States

    • A multi-project effort to contribute to our understanding of Pacific-North America plate boundary processes on inter-seismic and geologic time-scales. We particularly focus on forward models of stress and strain in the lithosphere based on geodetic, seismologic, and geodynamic information.

      • Platt, J. P., Kaus, B. J. P. and Becker, T. W.: The San Andreas Transform system and the tectonics of California: An alternative approach. Earth Planet. Sci. Lett., 274, 380-391, 2008. (PDF)
      • Becker, T. W., Schulte-Pelkum, V., Blackman, D. K., Kellogg, J. B., and O'Connell, R. J.: Mantle flow under the western United States from shear wave splitting, Earth and Planetary Science Letters, 247, 235-251, 2006. (PDF)
      • Becker, T. W., Hardebeck, J. L., and Anderson, G.: Constraints on fault slip rates of the southern California plate boundary from GPS velocity and stress inversions. Geophysical Journal International, 160, 634-650, 2005. (PDF).


    [news] [research] [publications] [group] [CV] [teaching] [downloads] [contact] [misc]
    [geodynamics] [seismology] [SEATREE] [downloads] [lab]
    [anisotropy] [global mantle dynamics] [subduction] [western US]
    Updated: November 17, 2009. (thorstinski at gmail dot com)