A Method for Waveform Inversion of Body-Wave Seismograms

• Main Author: Mellman, George Robert
• Format: Thesis
• Language: English
• Published: 1979
• Subjects: Bering Sea
• Online Access: https://thesis.library.caltech.edu/16338/; https://thesis.library.caltech.edu/16338/1/Mellman_GR_1979.pdf; https://resolver.caltech.edu/CaltechTHESIS:03212024-194510121

An iterative inversion method has been developed for the determination of velocity-depth structure and the estimation of seismic source parameters using the waveforms of far-field body-wave seismograms. The inversion is accomplished by minimizing an error function that expresses the difference between data and synthetic seismogram. This error function is constructed to be insensitive to absolute amplitudes and travel-times, and is thus a measure of wave­ form errors only. In the case where the source is known and the velocity-depth function is to be determined, the Modified First Motion method is used to express changes in the error function in terms of changes in the model parameters relative to some starting model. An approximate inverse is derived for this expression, which determines the model perturbation that minimizes the error function, Stability is provided through the inclusion of specific non-linear terms in the inverse. As an example of the application of the inversion technique, the fine structure of the crust-mantle transition is examined, using data from a Bering Sea refraction profile. In the case where earth structure is assumed known and the source parameters are to be determined, the source is represented as a small number of point shear dislocations. Using an inversion method quite similar to the one used for the earth structure problem, estimates are obtained of relative seismic moment, depth, fault orientation, source time function, and relative location for each point dislocation, The inversion method developed is applied to the study of the Borrego Mountain earthquake.