Travel time and amplitude analysis in seismic tomography

摘要: In cross-hole tomography straight lines connecting the source and receiver are often used to approximate true ray paths, thus linearizing inverse problem. A recent paper by Bregman et al. (1989a) has shown that this approximation may be very poor in regions of greatest interest where large velocity gradients cause significant curvature. The interpretation method presented iteratively traces updates model with perturbations obtained a damped least squares inversion travel time residuals. This presents modification so it applied first motion amplitudes for quality factor Q−1. After determining structure using inverted similar scheme. No additional tracing is required amplitude inversions. effect previously determined through taken into account variations due focusing defocusing effects not interpreted as being attenuation structure. Both methods here field data from experiment crystalline rock (Wong al., 1983). frequency range seismograms 1–6.6 kHz, allowing resolution on scale several meters. resulting image shows good agreement other geological geophysical data. Reversing placing boreholes opposite sides relative original reconstruction yields almost identical results, indicating interpolation scheme forward modeling biased final model. Synthetic Maslov calculated derived agree well waveform data, further confirming validity addition, results place absorptive same location most pronounced low-velocity features which correlate fractures boreholes. Highly transmissive also high-velocity regions.