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anomalous frequency value: any value of frequency that is negative (a physical impossibility) or that is positive with a magnitude greater than the Nyquist limit (the highest frequency allowed in time-sampled data).
anomalous phase change: any unexpected phase change. Example: the phase of a seismic wiggle trace should increase as the recording time increases. If the phase decreases momentarily, it is an anomalous phase change.
Hilbert transform: a special kind of filter applied to a stacked seismic trace which shifts all positive frequencies of an input signal by -90 degrees and all negative frequencies by +90 degrees, to create a complex trace consisting of a real trace, which is identical to the input stack trace, and an imaginary trace, which is the Hilbert transform of the real, stacked seismic trace. (Click here for detailed information about the concept of the Hilbert transform).
instantaneous frequency: the frequency of an oscillating function at a fixed point in time.
instantaneous phase: the phase of an oscillating function at a fixed point in time.
instantaneous seismic amplitude: the amplitude of a seismic wiggle trace at a fixed point in time.
monotonical: never changing in character. If a function increases monotonically, its rate of change is always positive and does not vary in magnitude.
reflection amplitude: a measure of the magnitude of the seismic response associated with an imaged rock interface. Typical reflection amplitude measurements are the amplitude of a peak or a trough of a seismic trace.
reflection phase: a measure of the polarity of a seismic reflection event associated with a rock interface. If a downgoing peak is reflected as a peak, the reflection phase for the interface is positive. If the peak reflects as a trough, the reflection phase is negative.
stratal surface : a surface of fixed depostional time. A bedding plane.
wavelet frequency: the frequency of a wavelet; all wavelets contain a spectrum of frequencies, not just one frequency. A wavelet is sometimes called a 20-Hz wavelet if the time interval between successive peaks (or troughs) of the wavelet is 50 ms because 1/50 ms = 20 Hz.
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