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Detecting temporal velocity changes using various methods

Detecting temporal velocity changes using various methods. Haijiang Zhang University of Science and Technology of China. Outline. Seismic tomography between different time periods Repeating earthquakes Coda wave interferometry Ambient noise. Different ray distribution on velocity models.

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Detecting temporal velocity changes using various methods

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  1. Detecting temporal velocity changes using various methods Haijiang Zhang University of Science and Technology of China

  2. Outline • Seismic tomography between different time periods • Repeating earthquakes • Coda wave interferometry • Ambient noise

  3. Different ray distribution on velocity models • Same theoretical models but with different ray distribution. • Separately Inverted models are different

  4. Different ray distribution on velocity models • Same theoretical models but with different ray distribution. • Jointly Inverted models are different

  5. Regularization in time

  6. Scattering: Scattering occurs when there are velocity heterogeneities in the medium with wavelengths on the order of λ of the wave.

  7. A simulation of 100 randomly-perturbed scatterers… Snieder et al., Science, 2002 Moving the scatterers (here, 1/40th of the distance shown, so the perturbation is visible) mostly changes the shapes and amplitudes of the waveforms…

  8. Waveforms measured in a granite sample at temperatures of 45°C (blue) and 50°C (red). Snieder et al., Science, 2002 Changing the matrix velocity, by contrast, introduces a shift (delay or advance) that increases with coda time.

  9. Near- and far-field effects of stress changes on cracks

  10. 3-m separation between two wells

  11. Near- and far-field effects of stress changes on cracks

  12. Repeating events-with (almost) the same waveforms

  13. Seismic velocity imaging and monitoring of volcanic areas using ambient seismic noise F.Brenguier (2008)

  14. Virtual seismic source reconstruction sensor Noise sources Shapiro et al. (2005)

  15. S 21° E 55°30 A case study: Piton de la Fournaise volcano, La Réunion island

  16. Temporal changes of seismic velocities using cross-correlations of seismic noise Synthetic velocity decrease

  17. Velocity changes on Piton de la Fournaise

  18. Velocity drops preceding eruptions Brenguier et al., Nature Geoscience, 2008

  19. Seismic velocity changes as a proxy for magma forcing Seismic velocities are strongly sensitive to crack density. O'Connell, R. J., and B. Budiansky (1974), Seismic Velocities in Dry and Saturated Cracked Solids, J. Geophys. Res., 79(35), 5412–5426

  20. Magmatic intrusive complex Link between temporal changes and structure • These velocity changes are linked to dilatation induced by stress changes

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