Talk:Reflection seismology

Wrong reflection and transmission coefficients

The reflection and transmission coefficients are still wrong - one of them is. Hence the equation relating R to T is not verified. Maybe an expert can decide which is which. My guess is we are talking about pressure indeed, so that R is fine and T is wrong (should be something like T = 2 Z1 / (Z1+Z0) ) and they are related by T=1+R. An expert is required to clarify this. Ferred (talk) 13:19, 29 January 2015 (UTC)

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Re: The equation for the Transmission coefficient: I have checked up on the equations posted on this page, and I am sorry to conclude that they have not been correct for quite som time. The equation is $T+R=1$. This does not present a problem regarding the aforementioned reflection coefficient -1 at the sea-air interface (from below). It is true that the incoming energy is almost entirely reflected. It is, however, important to remember that the amount of energy in the reflected and the transmitted waves does not only depend on the amplitude of the waves, but also on the geophysical parameters of the respective materials. The energy of a pressure wave in material 1 is given as $E_{1}=\alpha _{1}\rho _{1}\omega ^{2}A^{2}$, where $\alpha _{1}$ is the P-wave velocity in the material, $\rho _{1}$ is the density, $\omega$ is the angular frequency and $A$ is the pressure wave amplitude. Assuming energy conservation between the incoming wave and the reflected and transmitted wave it can be shown that the fraction of reflected energy is $E_{R}=R^{2}$ while the fraction of transmitted energy is $E_{T}={\frac {Z_{1}}{Z_{0}}}T^{2}$. Considering the extremely small acoustic impedance of air it is no surprise that the transmitted energy is negligible in the case of pressure wave reflection in the air water interface. Geologos (talk) 23:28, 25 November 2007 (UTC)

I have reverted the edits of Geologos because the equations were correct as they were. The precise form of the transmission coefficient depends on whether it is for pressure or particle velocity. The versions quoted are for pressure. Thunderbird2 (talk) 11:26, 26 November 2007 (UTC)

I apoligize for altering the content of the page so impolitely, but I believe that the section on reflection and refraction coefficients need altering to avoid misunderstandings of this sort. It is only at the second formula (the transmission coefficient) that it is told which parameter is actually dealt with, and it is put in parenthesis "(the ratio of transmitted to incident pressure)". I therefore suggest that it is clarified to avoid this potential ambiguity. A good name could be pressure reflection and transmission coefficients. A further possibility is to present both pressure and displacement R/T coefficients under separate headers and present their respective relations to the reflected and transmitted energy (To show how surprisingly little energy is actually reflected at real lithological interfaces). Geologos (talk) 20:32, 26 November 2007 (UTC)

Hi Geologos. There's no need to apologise. You corrected what you honestly believed to be an error, and I did the same, only in reverse. That's how Wikipedia works (see wp:bold) :-) Thunderbird2 (talk) 07:09, 27 November 2007 (UTC)

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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)

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.

You are absolutely correct that an independent branch of seismic technology has emerged using attributes of seismic data to directly identify presence of hydrocarbons. Go ahead and edit - I will contribute if required.

My comments (not'draft'): Bright spots, flat-spots, etc have been recognised (and drilled, sometimes successfully) for decades but direct targeting really took off in the late 90's with emergence of relatively inexpensive 3D data and the high quality of deep-water data eg West Africa. The emergence of more powerful computers also made analysis of pre-stack data practical eg Amplitude-Versus-Offset or 'AVO' which shows variation in amplitude with offset in the pre-stack gather (important to note that DHI's are often pre-stack attributes). We should distinguish between structural/stratigraphic attributes (basics), lithology (poro-perm) and DHI (fluids).--Okram999 (talk) 17:26, 4 January 2008 (UTC)

Spelling correction

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

 Done This is not the forum for spelling corrections.Blackrock36 (talk) 08:53, 20 February 2021 (UTC)

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)

Would it be better to say that "Reflection seismology is an application of seismology that uses..." rather than a branch? Or maybe "Reflection seismology is a method of exploration geophysics that uses seismology and reflected seismic waves to produce..."? I will try a variation on one of these and see how it sounds. GeoGreg 20:49, 31 January 2007 (UTC)

After some experimenting, I decided that producing "images" is not correct; reflection seismology estimates properties, a more general statement that is true of all geophysical methods. But anyone feel free to hack away. GeoGreg 20:57, 31 January 2007 (UTC)

 Done The current definition is suitable and sufficient. Blackrock36 (talk) 08:54, 20 February 2021 (UTC)

Applications

I'm thinking the application part could be updated to include some of the newer applications of reflection seismic, such as reservoir monitoring through time-lapse and characterisation through inversion. I don't know much about inversion, but I could try to write something about time-lapse. Any thoughts on this? Asbjørn L. Johansen 14:43, 7 August 2007 (UTC)

Vibroseis is a "cancelled" trademark

In Googling, I've found innumerable references that use it generically, and haven't been able to find a company by that name or any indication that it is actually a product name. If it's a trademark, what's the company that owns it? TESS shows it as registered to Continental Oil Company, but as "dead;" there are actually two trademark entries:

Registration Number 0737865 Registration Date September 18, 1962 (CANCELLED) IC 009. US 026. G & S: Electrical and Electronic Apparatus for Seismic Exploration for Oil-Namely, Electrically-Controlled Signal Generating Equipment, Magnetic Tape Recording Equipment, Amplification Equipment, Correlating Equipment, and Other Associated Electrical and Electronic Apparatus for Seismic Exploration. FIRST USE: 19610222. FIRST USE IN COMMERCE: 19610322

and

Registration Number 0735470 Registration Date July 31, 1962 Goods and Services (CANCELLED) IC 042. US 100. G & S: Geophysical Prospecting Service. FIRST USE: 19610222. FIRST USE IN COMMERCE: 19610322

I don't know what a "cancelled" trademark is. I wonder why it was cancelled? Dpbsmith (talk) 17:19, 8 August 2008 (UTC)

• If I had to guess, because it became common usage and Conoco didn't defend it (either due to choice or neglect). 174.29.145.167 (talk) 05:33, 30 March 2010 (UTC)

 Done It really is not important - Vibroseis was never a common alternative name for seismic vibrator vehicles anyway and this discussion is unnecessary. I removed the Vibrosies reference from the main page as it was a distraction and did not add value. Considering these comments on a cancelled trademark are from 10 years or more ago, they need to be removed.Blackrock36 (talk) 08:43, 20 February 2021 (UTC)

A 'vibroseis survey' is the predominant form of land seismic exploration operations in the world today where survey sizes in data easily run into petabytes. Vibroseis techniques marry perfectly into digital seismic processing, and vibroseis really took off in the 1970s with the introduction of minicomputers. Up to that point signal sources were all the various forms of 'dynamite' (ie explosive) , or weight drop 'Thumper' . I started work in 1974 in seismic processing on onsite systems J R Spigot (talk) 16:12, 8 August 2022 (UTC)

Diagram of dubious provenance

A diagram is this article purports to show some effect of a landmine. All parts including the axes are unlabelled. There is no telling what names some people are given or choose but the WP name of the loader of the diagram suggests a lack of propriety. Failing validation it should be deleted.--SilasW (talk) 21:41, 15 June 2009 (UTC)

GSI

I would like to point out as a former employee of GSI, they are not owned in any way by WesternGeco (whom I also used to work for). GSI was bought out by Tesla Exploration.

• As far as I know, GSI was bought by Halliburton in the late 1980s and merged with Geosource into Halliburton Geophysical Services (HGS). A few years later (about 1993), HGS was sold to Western Geophysical, then a division of Western Atlas. In 1998 or so, Western (as part of Western Atlas) was sold to Baker Hughes. Baker put Western Geophysical into a JV with Schlumberger's Geco-Prakla in 2000, forming WesternGeco. As of 2006, I think, WesternGeco is 100% Schlumberger. Did Tesla buy part of GSI? If so, I've forgotten it. But I was on the Western side of the Western-HGS merger, so I might not know all the details. 174.29.145.167 (talk) 05:31, 30 March 2010 (UTC)

Questions on History

Could someone expand the history section with some information about when 3D seismic became prevalent in the oil industry? Did everyone have 3D seismic for their reservoir modeling by the 60s, for example? —Preceding unsigned comment added by 134.32.11.71 (talk) 09:23, 12 August 2010 (UTC)

3D surveys only became viable during the 1980s due to economics, computational demands and even more practical things such as the volume of data being recorded vs. the volume of data that a magnetic tape could hold. I'm going to try and work on some of this article as it is really important. Nwhit (talk) 19:20, 20 February 2012 (UTC)

Moving forward with this article

At the moment, I am hoping to expand the section on applications and work on the current content that is there. Hopefully this is how the section will end up looking:

2 Applications

2.1 Near-surface

2.2 Hydrocarbon exploration

2.2.1 Land survey acquisition

2.2.2 Marine survey acquisition (streamer)

2.2.3 Marine survey acquisition (ocean-bottom incl. 4D)

2.2.4 Seismic data processing

2.2.5 Geological interpretation

2.2.6 Seismic attribute analysis

2.3 Crustal studies

Once this is done, I can work on the rest of the article. If anyone has any comments, they're most welcome.Nwhit (talk) 18:08, 29 February 2012 (UTC)

I've now managed to remove the vast sections of unreferenced material from this section and replaced it with referenced material. This will still need adding to, but it's a start.Nwhit (talk) 11:25, 12 March 2012 (UTC)

A useful image?

A three dimensional echo sounding representation of a canyon under the Red Sea by survey vessel HMS Enterprise.

Think this image might be useful somewhere here? Don't know enough about the subject to know where Mrjohncummings (talk) 15:13, 3 July 2013 (UTC)

It's a pretty picture, but not one created using reflection seismology. It might find a good home here: https://en.wikipedia.org/wiki/Echo_sounding --Shoobydo (talk) 18:30, 23 September 2013 (UTC)

Why not appropriate to archaeology?

Shouldn't the article explain why this technology is not used in archaeology surveying, in addition to GPR? I don't know the answer. David Spector (talk) 15:14, 18 May 2017 (UTC)

For any geophysical technique, I suppose that the applications for which it is not useful will always greatly outnumber those for which it is useful. If we start going down that path, we might dedicate a lot of article space to explain why it is not used for X, Y, or Z. Also, the literature is probably scant to none describing most inappropriate applications. I suspect that GPR is so much faster and cheaper than seismic, so if the target is shallow enough to show up on GPR, why would anyone use seismic? That said, the article might better describe why it is so useful in some applications, to help the reader understand why it is not used in others. Thanks for your comment. Plazak (talk) 18:29, 18 May 2017 (UTC)

Sorry, just thought I would add to this since I just added material to minicomputers relating to seismic exploration ...

Reflection seismic is appropriate for imaging of deep subsurface for hydrocarbons, so in the regions of thousand of feet below.

In specific cases of 'site survey seismic' the depth can be relatively shallow, hundreds of feet, but this is check for shallow gas when deciding the specific location to site a drilling rig. Shallow reflection surveys are also used for mapping coal seams.

In archaelogical terms the target is only a matter of a few feet below the surface.

Overall the article isn't very clear in many places. J R Spigot (talk) 16:03, 8 August 2022 (UTC)

Your suspicion sounds likely to me, although a reliable reference would be useful so it can be added to the article.

However, I do not agree with your reductio ad absurdum rhetoric that attempts to prove your suspicion. The number of possible applications is not, I believe, very many, and in fact archeological surveying is the only natural application I can think of that is not already covered by the article. Please provide a list of example X, Y, and Z applications of reflection seismology if you care to convince me of your logical argument. David Spector (talk) 00:00, 19 May 2017 (UTC)

Reflection seismic is not used to search for ores of gold, silver, copper, or other metals. It is not used to detect radioactive elements. Seismic is not used to detect submarines, lost oil wells, saline groundwater intrusion, or saline soil contamination. Other geophysical methods are much better in each of these applications. I also don't understand why you consider archaeology a "natural application" of refection seismic. Although I have no experience in using either seismic or GPR in archaeology, I suspect that GPR would be capable of picking up subtler changes in the shallow subsoil (disturbed soil, filled-in excavations, smaller objects that do not generate a coherent seismic reflection) than would be possible with reflection seismic, which requires quite an abrupt change to generate a reflection, and has difficulty imaging nonlayered features. Is my suspicion correct? We run into the what is called "the file-drawer problem." As I alluded to above, scientific journals prefer to publish articles on methods that work, and do not often print articles of the type "I tried this method here, and it failed miserably." Regards. Plazak (talk) 01:09, 19 May 2017 (UTC)

Plazak, Thank you for the interesting list. But most of your items are simply invalid: no educated person would even imagine that sound waves could be used to detect radioactivity. But I have been watching the Time Team TV programs, in which associates of the team routinely use resistivity, magnetic field, and GPR technologies to perform preliminary scans of fields prior to digging in them. It is clear that they have rejected sound-based forms of radar (either adjustable-frequency SONAR or reflective seismology), and I consulted WP to find out why they did so. I believe that the boundaries between packed soil and rock would be perfect for detection by reflective seismology (although such boundaries might obscure deeper boundaries below them), so why would archaeologists, who are primarily interested in visualizing buried stone walls, not want to use it as one of their technologies, and perhaps even as their first (quickest/preliminary/overview) survey technology? If the technology won't work, or if it is too expensive, that fact belongs in the article, for the benefit of those, like me, who wonder why it is not used for this obvious application. David Spector (talk) 20:06, 21 May 2017 (UTC)

You are certainly right that the soil/bedrock interface is an excellent reflector in both reflection and refraction seismic. You are also correct that ringing from the surface layer can obscure deeper interfaces. As for archaeology, you still run into the "file-drawer problem." If you do find something on the subject, I would bet that it mentions the difficulty seismic has in imaging non-layered objects such as walls. But all this is beside the point: if the subject is of interest to you, it will probably interest others, and therefore you are right that it belongs in Wikipedia. Regards. Plazak (talk) 23:55, 21 May 2017 (UTC)

A final thought: perhaps archaeology simply hasn't yet discovered reflection seismology. Perhaps the specific technology used to find oil and gas deposits is not exactly a technology that would be of value in archaeology, but perhaps sound is exactly the right stimulus to use in mapping underground features involving substances of different densities such as stone walls, wooden posts, and layers of refuse. Current technologies in use in archaeology include magnetic field measurements, electric resistance, and various radar methods (which, of course, are based on radio waves). When some archaeologist or student first uses a mapping technique based on the passage of varying-frequency sound waves through soil and rock, perhaps an accurate and high-definition view of the underground scene may turn out to revolutionize the discipline. I consider this article open to future extension in this direction. David Spector (talk) 18:57, 12 August 2018 (UTC)

Use of sound is common in underwater archaeology. Dondervogel 2 (talk) 19:36, 12 August 2018 (UTC)

If anyone thinks something should be included in the article, their argument becomes much stronger of a reliable source can be cited.· · · Peter Southwood ^(talk): 14:59, 15 June 2022 (UTC)

I didn't take part in the earlier discussion, but now that I look at it, the usefulness of the technique depends on the necessary resolution and that depends on the frequency of the seismic source used. Reflection seismology is very occasionally used in site investigations in engineering geology. I was involved with the investigation at the Heysham nuclear power station for the proposed Dry Buffer Store back in 1989 and that used the seismic reflection method to identify the location of faults in the subsurface - necessary for the ground rupture study for potential earthquakes at the site. The method in those circumstances has trouble detecting any changes of less than a few metres, so not useful for most archaeological investigations I would think. Mikenorton (talk) 16:48, 15 June 2022 (UTC)

Simplify.

We have to remember that most readers do not have degrees in geology, so we should write simply enough to get the point across and leave the details to the grad students and professors. BeenAroundAWhile (talk) 20:28, 25 October 2017 (UTC)

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Marine section: ways to avoid disturbing marine mammals

More inforamtion. I would like to add some information on ways to avoid disturbing marine mammals whilst surveying. See section below.

In 2017, IOGP recommended that, to avoid disturbance whilst surveying:

• Protective measures are employed to address site-specific environmental conditions of each operation to ensure that sound exposure and vessel traffic do not harm marine mammals.*
• Surveys planned to avoid known sensitive areas and time periods, such as breeding and feeding areas. *
• Exclusion zones are typically established around the seismic source to further protect marine fauna from any potentially detrimental effects of sound. The exclusion zone is typically a circle with a radius of at least 500 meters around the sound source. *
• Trained observers and listening devices are used to visually and acoustically monitor that zone for marine mammals and other protected species before any sound-producing operations begin. These observers help ensure adherence to the protective practices during operations and their detailed reports provide information on the biodiversity of the survey area to the local governments.*
• Sound production typically begins with a “soft-start” or “ramp-up” that involves a gradual increase of the sound level from the air gun source from a very low level to full operational levels at the beginning of the seismic lines – usually over 20 to 40 minutes. This soft-start procedure is intended to allow time for any animal that may be close to the sound source to move away as the sound grows louder.*

Seems like a good idea - I know a lot of acquisition outfits already do this stuff. Mikenorton (talk) 15:16, 5 October 2018 (UTC)

Marine section: General discussion on impacts on marine mammals

I'm not sure that the current content in the marine section is totally relevant at present. There are a few short paragraphs to illustrate that seismic is disruptive and a quote from an IAGC report that's its not, presumably for balance. However, this is a very complex discussion depending upon which perspective you take and simple extracts from research always need to be carefully considered. For example, an extract from an IAGC report (IAGC being a vested interest group for the seismic industry immediately does not sit right as an independent source) and also the claim as quoted that seismic does not injure mammals (I paraphrase here) is not a recommendation either (i.e. does it upset, distress, displace, disrupt migration, disrupt breeding, etc, etc...?). This report is also dated from 2012 and is really old research unlikely to be current thinking.

I propose to remove the text from the Marine section starting from "A study has shown...." through to "...injury to any marine mammal species." and to include a more general discussion on what current thinking is on this issue and how it is managed such as with impact assessments and so on.

Also this is an Earth Science /WikiProject Geology subject and too much detail concerning environmental science is deviating away from its main purpose. Of course, environmental discussions should be had here but at a more general level and we should prompt the reader to look elsewhere for more detailed information on these issues.Blackrock36 (talk) 14:16, 21 February 2021 (UTC)

References