High resolution seismic tomography with the generalized Radon transform and early arrival waveform inversion

Traveltime tomography is an important imaging tool in oil and gas exploration and earthquake seismology. However, the spatial resolution of traveltime tomograms is inherently restricted because of the finite-frequency effects in the data and the high-frequency approximation in ray-based tomography. In this dissertation, the generalized Radon transform (CRT) is used to derive the resolution limits for wavepath traveltime tomography, and a new imaging algorithm is developed based on the resolution formula. In addition, I develop and test a new imaging algorithm, early arrival waveform tomography (EWT) algorithm and show that it combines good convergence with high resolution capabilities.; The Rytov approximation that expresses phase residuals as an explicit function of the slowness perturbations is also related to the CRT. Using Beylkin's formalism, the corresponding inverse CRT is obtained to give the slowness model as an explicit function of the phase residuals. A slowness resolution formula is obtained that explicitly gives the slowness perturbation function as a product of the frequency and the traveltime gradient obtained by ray tracing. I denote tomograms based on this new development CRT tomograms. Resolution limits are obtained for models estimated from several types of data: first-arrivals from a crosswell experiment, refraction data associated with diving-wave arrivals and earthquakes. A fat-ray traveltime tomography algorithm is derived that automatically limits the size of pixels based on diffraction theory. These new theoretical formulae provide powerful tools for realistically estimating slowness resolution in tomograms and imaging the earth's velocity distribution.; Even CRT tomography has limits when multiarrivals (e.g., diffraction events) interfere with one another at early times. In this case, I developed an alternative to waveform tomography which only predicts the early arrivals by finite-difference solutions to the wave equation. I denote this new method EWT. By fitting the early arrivals, EWT naturally takes into account more general wave propagation effects, such as diffractions and wavepath averaging. This means there is less conflict between the observed and predicted data, so a wider range of slowness wavenumbers can be estimated compared to traveltime tomography. (Abstract shortened by UMI.)...