Distinguishing horizontal/vertical discontinuities

Problems in Exploration Seismology and their Solutions

Series	Geophysical References Series
Title	Problems in Exploration Seismology and their Solutions
Author	Lloyd P. Geldart and Robert E. Sheriff
Chapter	6
Pages	181 - 220
DOI	http://dx.doi.org/10.1190/1.9781560801733
ISBN	ISBN 9781560801153
Store	SEG Online Store

Problem 6.12

Pautsch (1927) showed that a horizontal or vertical interface could give identical first-arrival curves (Figure 6.12a). Add secondary refractions and reflections to show how they can distinguish between the two cases.

Background

At Pautsch’s time only first arrivals were observed and hence interpretation had to be based on them. Today we also observe refraction events (secondary arrivals or secondary refractions) that are not first arrivals (see problem 6.20).

Solution

For the vertical interface in Figure 6.12a(ii) there will be a direct wave plus a reflection directed back toward the source. For the horizontal interface, there is also a reflection and a refraction (head wave), the refraction curve being tangent to the reflection curve at the critical distance. These additional curves distinguish between the two cases. Also, if we move the source, the bend in the curve moves in (ii) but not in (i).

Figure 6.12a.  Models that give identical traveltime curves.

Figure 6.12b.  Models that give identical traveltime curves.

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Table of Contents (book)

Also in this chapter

• Characteristics of different types of events and noise
• Horizontal resolution
• Reflection and refraction laws and Fermat’s principle
• Effect of reflector curvature on a plane wave
• Diffraction traveltime curves
• Amplitude variation with offset for seafloor multiples
• Ghost amplitude and energy
• Directivity of a source plus its ghost
• Directivity of a harmonic source plus ghost
• Differential moveout between primary and multiple
• Suppressing multiples by NMO differences
• Distinguishing horizontal/vertical discontinuities
• Identification of events
• Traveltime curves for various events
• Reflections/diffractions from refractor terminations
• Refractions and refraction multiples
• Destructive and constructive interference for a wedge
• Dependence of resolvable limit on frequency
• Vertical resolution
• Causes of high-frequency losses
• Ricker wavelet relations
• Improvement of signal/noise ratio by stacking

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