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Abstract

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.

Item Type:	Thesis - PhD
Authors/Creators:	Blackburn, Gregory John
Keywords:	Seismic reflection method, Geology
Copyright Holders:	The Author
Copyright Information:	Copyright 1982 the Author – 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).
Additional Information:	Thesis (Ph.D.)--University of Tasmania, 1983. Bibliography: l. R.1-R.10
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