whole_BlackburnGregoryJohn1983_thesis.pdf (11.6 MB)
Some problems with seismic reflection techniques
thesisposted on 2023-05-27, 06:51 authored by Blackburn, Gregory John
Non-zero offset raypath tracing of primary P waves over a suite of geologically complex two-dimensional models illustrates that large errors occur in the conversion of stacking velocities to vertical velocities. Consequently (1) stacking velocities may not be consistent for seismic lines shot over the same area for different field configurations, (2) stacking velocities can vary greatly for a given spread length and different shot offsets, (3) rapid lateral changes in stacking velocities due to geological factors may disguise velocity information from horizons overlain by irregularities, (4) the customary assumption that stacking velocities approximate root mean square velocities is not valid in areas of geological complexity, (5) fictitious time shifts and consequent timing and velocity errors are introduced when conventional replacement statics are used, and (6) statics are time variant and surface inconsistent so that appropriate corrections should be made according to layer depth. Simple mathematical expressions are derived for velocity and depth migration determination in both steeply dipping and complicated overburden environments. Model studies show that the amplitude, frequency and wavelet characteristics of a reflector are dependent on both the reflector and overlying formations and may preclude definition of the reflecting surface. The use of CDP methods is detrimental in preserving these essential parameters. Interference due to thin layers results in reflectivities, transmissivities and mode conversion that depend on the layering properties, frequency and angle of the incident plane wave. Increased resolution of thin beds can be obtained by using the converted PS or SS waves.
Rights statementCopyright 1982 the Author ‚Äö- The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s). Thesis (Ph.D.)--University of Tasmania, 1983. Bibliography: l. R.1-R.10