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There are different seismic sources for both land and marine acquisition surveys. Measuring the spectral characteristics (phase, frequency, amplitude, etc.) is a critical part of evaluating the usefulness of the source and is quite difficult to measure accurately (especially on land). We always seek to generate an impulse (or a Dirac spike).

All this said, my question is this: how and why do different frequencies retain various phase delays and amplitudes? Is this a phenomenon that does not occur the instantaneous moment the source is used...? I used Seismic Unix to generate the figure below - note that a phase diagram is not included here, but you already know that there some degree of phase delay/difference associated with each frequency (note: the horizontal axis is frequency and vertical is amplitude):

enter image description here

If my question seems vague, think of it this way. Let's say I (and my source) are in an infinite, elastic, and homogeneous medium. I set off my source (note that it is NOT a perfect impulse), and the result may look like what is pictured below. What causes frequencies to retain different amplitudes? What causes the phase delay associated with each frequency? I know I've included a lot here, regardless, any insight/comments are greatly appreciated.

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