Seismic Interferometry, Nonlinear Tomography, Nonlinear Migration and Retrospective Seismology

Usually seismic interferometry (often called Green's function estimation from ambient noise correlation) is used to perform seismic tomography of the Earth's subsurface using only background vibrational noise. Seismometers can be turned into virtual (imagined) sources of energy that produce real seismograms. Real energy sources (e.g., earthquakes or active-source seismic shots) can be turned into virtual seismometers perhaps deep inside the solid Earth. Interferometry also provides novel schemas for computational modelling of acoustic, elastic and electromagnetic phenomena, and embodies completely new Optical Theorems of Physics. In this talk I will first focus on a new method for ambient noise tomography which constructs quite different subsurface information compared to existing tomography algorithms. I will then focus on two of the most recent interferometric advances using the theory of Source-Receiver Interferometry (SRI). First, SRI allows us to record earthquake seismograms on seismometers that were installed (perhaps years) after the earthquake occurred - a result that can be generalised to acoustic, electromagnetic, electro-kinetic and a range of other phenomena. This offers the benefit of hindsight in observational science since receivers can be physically installed in the knowledge of where an event of interest has taken place, and recordings of the event can still be obtained. Second, SRI also provides new generalised, nonlinear methods to form seismic images of the Earth's interior using active sources. In industrial geophysics this provides the possibility that in future we may achieve so-called super-resolution - resolving structures at sub-wavelength scale. In addition, SRI leads to data-driven methods to decompose observed multiply-scattered wavefields into their constituent inter-scatterer components. I will introduce the theory of SRI, then these various results, and will discuss their applications and implications. ASSOCIATED REFERENCES: A. Curtis, Y. Behr, E. Entwistle, E. Galetti, J. Townend, S. Bannister, 2012. The benefit of hindsight in observational science: retrospective seismological observations. Earth and Planetary Science Letters,vol. 345-348, pp. 212-220 A. Curtis and D. Halliday, 2010. Source-receiver wave field interferometry. Physical Review E, Vol.81, No.4, pp. 046601-1 - 046601-10. doi: 10.1103/PhysRevE.81.046601 E. Galetti and A. Curtis, 2012. Generalised receiver functions and seismic interferometry. Tectonophysics. doi: 10.1016/j.tecto.2011.12.004 D. Halliday and A. Curtis. An interferometric theory of source-receiver scattering and imaging. Geophysics, Vol.75, No.6 pp.SA95–SA103. doi: 10.1190/1.3486453 S. King, A. Curtis and T. Poole, 2011. Interferometric velocity analysis using physical and nonphysical energy. Geophysics, Vol.76, No.1, pp. SA35-SA49, doi: 10.1190/1.3521291 S. King and A. Curtis, 2012. Suppressing nonphysical reflections in Green's function estimates using source-receiver interferometry. Geophysics, 77(1), pp. Q15-Q25. doi: 10.1190/GEO2011-0300.1 M. Ravasi and A. Curtis. Nonlinear scattering based imaging in elastic media: theory, theorems and imaging conditions. Geophysics 78(3), pp. S137–S155, doi:10.1190/GEO2012-0286.1