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Table 1. This table provides a checklist of factors that affect amplitudes. Factors in bold are more important.

Seismic Acquisition (Source) FIGURE 1 • FIGURE 2

Factors

Comments

Magnitude

F1) Source Strength

Size of dynamite, number of working vibrators, number of sweeps, etc.

Moderate

F2) Source Coupling

Source in dry sand, weathering (poor coupling), bedrock, wet soil (good)

Moderate

F3) Source Arrays

Designed to attenuate noise but also attenuates dipping primaries

Minor

F4) Source Ghost

Reflected signature with opposite sign at free surface

Minor

The Earth FIGURE 1 • FIGURE 2

Factors

Comments

Magnitude

F5) Discontinuous Trans

When RC large enough (Volcanics, Salt) underlying events not visible

Mod-Major

F6) Curved Ray

Spherical spreading of energy is the MAJOR effect, factor of 10 or more

MAJOR

F7) Tuning

Tuning can be major, up to factor of 2, at pinchouts can be down to zero

Mod-Major

F8) AVA

AVA gas effects can be up to a factor of 5

Mod-Major

F9) Curved Reflectors

Focusing and defocused - minor, exceptions include salt lens - mod-major

Minor

F10) Rugosity

At seismic wavelengths most geologic surfaces are "mirror" smooth

Minor

F11) Interbed Multiples

If RC contrasts are high then can be moderate problem, generally minor

Minor

F12) Absorption

Loss of energy to heat, weighted towards high frequencies

Minor

F13) Scattering

Loss of energy due to specular reflections, weighted towards high frequency

Minor

Seismic Acquisition (Receiver) FIGURE 1 • FIGURE 2

Factors

Comments

Magnitude

F14) Receiver Coupling

Geophones dampened on dry soil, buried or wet soil couples well

Moderate

F15) Surface Multiples

Negative RC at surface, then positive at base weathering

Minor

F16) Receiver Ghost

Reflected RC with opposite sign at free surface, changing surface RC

Minor

F17) Receiver Strength

Poorly placed geophones, partial loss of array

Minor

F18) Receiver Arrays

Designed to attenuate noise but will also attenuate dipping primaries

Minor

F19) Geophone

Response is a filter that reduces amplitudes

Minor

F20) Dynamic Range

Pre-1990 with limited 12-15 bit recorders / filters Moderate, now Minor

Minor

F21) S&R "Skips"

Missing ground positions / offsets, effects # traces and frequency content

Mod-Major