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Seismic Trace Attributes
As the name implies these attributes are calculated from the values above and below each sample within a window in the same trace.
NB! Hovering over the name of an attribute in the drop-down list will display a short description of this attribute.
Complex Trace Attributes
A seismic trace (amplitude), x(t) is real, but can be viewed as the real part of an analytical trace: z(t) = x(t) + i*y(t), where i is the imaginary unit and y(t) is the Quadrature Amplitude.
The Quadrature Amplitude is calculated by taking the Hilbert transform of the Amplitude: y(t) = H{ x(t) }.
From this definition a whole range of attributes can be derived.
Quadrature Amplitude
The imaginary part of the complex seismic trace. Equals a 90 degrees phase shift of the real seismic trace.
Envelope
Also know as reflection strength, instantaneous energy and magnitude.
It is defined as the absolute value of the complex trace: Envelope = √(x^2+y^2).
Mainly useful for
- Bright spots
- Gas accumulation
- Sequence boundaries, major changes or depositional environments
- Thin-bed tuning effects
- Unconformities
- Major changes of lithology
- Local changes indicating faulting
Two Seismic Lines or Seismic Brick Cubes that are the same except for the phase will have the same envelope.
Instantaneous Phase
The Instaneous Phase is defined as: φ=arctan(y/x).
Reveals weak and strong events with equal strength, thereby improving reflector continuity and enhancing the visual appearance of edges.
Commonly displayed with a wrapped Color Table since the extreme values: -pi and pi refer to the same phase.
Cosine of Instantaneous Phase
Same characteristic as Instantaneous Phase but avoids the problem with the discontinuity at -pi,pi.
Commonly used for interpretation in areas with weak seismic.
Apparent Polarity
The sign (+/- 1) of the seismic trace at the peaks of the Envelope.
In a noisy seismic area the event continuity can be clearer on the apparent polarity than on the original seismic.
It is therefore sometimes used as input to auto-trackers.
Dominant Frequency