Maximising the lateral resolution of near-surface seismic refraction methods

서지정보

· 발행기관 : 한국지구물리.물리탐사학회
· 수록지 정보 : 지구물리와 물리탐사 / 12권 / 1호 / 85 ~ 98페이지
· 저자명 : Derecke Palmer

초록

The tau-p inversion algorithm is widely employed to generate starting models with most computer programs,
which implement refraction tomography. This algorithm emphasises the vertical resolution of many layers, and as a result, it
frequently fails to detect even large lateral variations in seismic velocities, such as the decreases which are indicative of shear
zones. This study demonstrates the failure of the tau-p inversion algorithm to detect or define a major shear zone which is 50m
or 10 stations wide. Furthermore, the majority of refraction tomography programs parameterise the seismic velocities within
each layer with vertical velocity gradients.
By contrast, the Generalized Reciprocal Method (GRM) inversion algorithms emphasise the lateral resolution of
individual layers. This study demonstrates the successful detection and definition of the 50m wide shear zone with the
GRMinversion algorithms. The existence of the shear zone is confirmed by a 2Danalysis of the head wave amplitudes and by
numerous closely spaced orthogonal seismic profiles carried out as part of a later 3D refraction investigation. Furthermore, an
analysis of the shot record amplitudes indicates that a reversal in the seismic velocities, rather than vertical velocity gradients,
occurs in the weathered layers.
The major conclusion reached in this study is that while all seismic refraction operations should aim to provide as accurate
depth estimates as is practical, those which emphasise the lateral resolution of individual layers generate more useful results for
geotechnical and environmental applications. The advantages of the improved lateral resolution are obtained with 2D
traverses in which the structural features can be recognised from the magnitudes of the variations in the seismic velocities.
Furthermore, the spatial patterns obtained with 3D investigations facilitate the recognition of structural features such as faults
which do not display any intrinsic variation or ‘signature’ in seismic velocities.

참고자료

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