Talk:Reflection seismology

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Re: the equation for transmission coefficient: it is T = 1 + R. For those of you familiar with marine seismic data, the reflection coefficient at the ocean surface is, for all practical purposes, -1, and (practically) no energy is transmitted to the air, the impedance contrast being so great. Thus, the equation for T cited above gives the correct value for T, namely 0. Note that R = 1 occurs in the opposite situation (air to water), as air has an impedance of effectively 0 compared to water or rock. This gives T = 2. I think the question is "what exactly is the amplitude we are measuring"? I will try to clarify that. Gwimpey 03:57, Jan 28, 2005 (UTC)

You are right, it depends on what you are measuring. If you measure pressure, then pressure is zero on the free surface, hence reflected wave must have opposite sign to the incident wave to yield that zero, so that R=-1. Thus for pressure T=0, as you say. Conversely, at a very hard surface, displacement is zero, while pressure has a maximum. Thus for pressure we have R=1, the resultant pressure being twice that of the incident wave. Since pressure is continuous across the interface, this creates the wave in the second medium which has twice the pressure amplitude of the incident wave. Thus T=2 is correct. It is reverse for displacement.

Now I have an entirely different question. When talking about environmental impact, shouldn't we mention that in the past explosive sources were widely used offshore, but have been banned for some years now? Unfortunately, I do not know legal or historical aspects of this. Can anyone comment?BorisG 13:47, 13 November 2005 (UTC)

That would be a good idea. As with many resource activities, impact is much less today than in the past. But finding the specifics may be hard. I don't know where this would have been documented. Gwimpey 18:07, 28 December 2005 (UTC)

[edit] Direct Hydrocarbon Indicators

'Seismic technology does not allow the direct detection of hydrocarbons, but it is used by geologists and geophysicists who interpret the data to distinguish the presence of structural traps that could potentially contain hydrocarbons' This sentence is not strictly true. Firstly, in seismic data processing we attempt to search for and enhance images artefacts called 'direct hydrocarbon indicators'. usually seen as a 'bright spot' or 'dim spot' on a stcaked seismic section. Secondly, seismic data processing has long since ceased to be solely about structural interpretation. Nowadays a significant amount of effort is made to search for various amplitude anomalies to act as lithology and property (egs. porosity, permeability etc) identifiers. If no-one objects I will consider a re-write over the next few days.

[edit] Spelling correction

Made on minor spelling correction while reading this article. Shanneranner 20:33, 22 September 2006 (UTC)

[edit] Introduction defining the topic

“Reflection seismology or seismic reflection is a branch of seismology that uses reflected seismic waves to produce images of the Earth's subsurface.” When reading this article, it gives more an impression of describing reflection seismology as a method – with applications, to collect subsurface information (data). To interpret the data, scientists make use of seismology (“the scientific study of earthquakes and the movement of waves”) and Exploration geophysics among other disciplines. --Roarjo 10:11, 12 November 2006 (UTC)