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Fall 2009 Seminars

Friday, November 20, 2009
Inverse Problems Seminar
Speaker: Steve Roecker, Earth and Environmental Sciences (RPI)
Title: Full Waveform Teleseismic Tomography: Imaging the Earth with Distant Earthquakes
Location: Amos Eaton Rm 402
Time: 12:00 PM

Abstract:
Analyses of seismograms recorded by regional seismic networks of body waves generated by sources at teleseismic distances have made tremendous contributions to our understanding of the Earth's interior. In this talk I will describe an adaptation of a 2D spectral domain finite difference waveform tomography algorithm previously used in active source seismological imaging to the case of a plane wave propagating through a 2.5D viscoelastic medium in order to recover P and S wavespeed variations from body waves recorded at teleseismic distances. A transferable efficacy that permits recovery of arbitrarily heterogenous models on moderately sized computers provides the primary motivation for choosing this algorithm. Synthetic waveforms can be generated either by specifying an analytic solution for a background plane wave in a 1D model and solving for the source distribution that would produce it, or by solving for a scattered field excited by a plane wave source and then adding the background wavefield to it. Because the former approach typically involves a concentration of sources at the free surface, the latter tends to be more stable numerically.We adapt a gradient approach to solve the inverse problem to maintain tractability; calculating the gradient does not require much more computational effort than does the forward problem. The waveform tomography algorithm can be applied in a straightforward way to perform receiver function migration and travel time inversion in situations where a priori information about background wavespeeds may make a complete full waveform approach untenable.

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