Hello-- I would like to generate a synthetic seismic trace using the real-valued Ricker wavelet. (Other wavelets could also be used.) Normally I think that this should involve a convolution operation. However, I would like to ensure that the synthetic trace has a constant (and known) Q-value. I would like to find a monograph/book/paper or some other type of procedure to efficiently generate this synthetic trace. Any suggestions?

# Generation of synthetic seismic trace with known Q-value

Started by ●March 14, 2010

Reply by ●March 14, 20102010-03-14

On 14 Mar, 18:23, Nicholas Kinar <n.ki...@usask.ca> wrote:> Hello-- > > I would like to generate a synthetic seismic trace using the real-valued > Ricker wavelet. �(Other wavelets could also be used.) �Normally I think > that this should involve a convolution operation. �However, I would like > to ensure that the synthetic trace has a constant (and known) Q-value. > > I would like to find a monograph/book/paper or some other type of > procedure to efficiently generate this synthetic trace. �Any suggestions?Seismic traces are usually modeled using some Finite Difference or Ray Tracing scheme. Either way, the constant Q question is irrelevant, as all kinds of physical effects mess the signal up. Decide on a Ricker wavelet and use it. No need to fuzz things up with Q values; you will have more than enough other stuff to worry about. Rune

Reply by ●March 14, 20102010-03-14

Hello Rune-- Thank you for your response.> > Seismic traces are usually modeled using some Finite > Difference or Ray Tracing scheme. Either way, the > constant Q question is irrelevant, as all kinds of > physical effects mess the signal up. > > Decide on a Ricker wavelet and use it. No need to > fuzz things up with Q values; you will have more > than enough other stuff to worry about.Yes - you are right about the physical effects, and this is what I would normally do if I wanted a "realistic" seismic trace: use finite-difference or ray-tracing algorithms. However, I am reading a book "Seismic Inverse Q Filtering" by Y. Wang, and the author describes how to build an extremely simple seismic trace with a known Q value to test an inverse seismic Q filtering algorithm. The idea is to generate a (non-realistic) simple seismic trace. I've tried to implement this algorithm, but I find that some of the salient details of the implementation are tricky. Could I send you some further information via e-mail to read? Then perhaps we could summarize on the newsgroup what would be required to fully implement this synthetic algorithm. Thanks Rune.

Reply by ●March 14, 20102010-03-14

On 14 Mar, 19:10, Nicholas Kinar <n.ki...@usask.ca> wrote:> Hello Rune-- > > Thank you for your response. > > > > > Seismic traces are usually modeled using some Finite > > Difference or Ray Tracing scheme. Either way, the > > constant Q question is irrelevant, as all kinds of > > physical effects mess the signal up. > > > Decide on a Ricker wavelet and use it. No need to > > fuzz things up with Q values; you will have more > > than enough other stuff to worry about. > > Yes - you are right about the physical effects, and this is what I would > normally do if I wanted a "realistic" seismic trace: use > finite-difference or ray-tracing algorithms. > > However, I am reading a book "Seismic Inverse Q Filtering" by Y. Wang, > and the author describes how to build an extremely simple seismic trace > with a known Q value to test an inverse seismic Q filtering algorithm. > > The idea is to generate a (non-realistic) simple seismic trace. �I've > tried to implement this algorithm, but I find that some of the salient > details of the implementation are tricky. > > Could I send you some further information via e-mail to read?No.>�Then > perhaps we could summarize on the newsgroup what would be required to > fully implement this synthetic algorithm.Just browsing the table of contents of the book, http://www.amazon.com/Seismic-Inverse-Filtering-Yanghua-Wang/dp/1405185406/ref=sr_1_1?ie=UTF8&s=books&qid=1268595741&sr=8-1#reader_1405185406 sends cold shivers down my spine. The author's premise seems to be that there exists 'a' mathemathical model that influences the Q factor of the trace. Then he goes on to list almost a dozen different models for the effect (see the list of subchapters in chapter 3). That alone sets off all the alarms in my mind. I used to do those kinds of things ages ago and my experience is that the earth is a random medium in every sense of the word. Unless you sample it directly - drill a hole and dig stuff out of it - one does not know much. While any of the proposed models might be defended in one setting, the reality is that there are gazillion other situations in the same survey where the model is invalid. Rune

Reply by ●March 14, 20102010-03-14

> > Just browsing the table of contents of the book, > > http://www.amazon.com/Seismic-Inverse-Filtering-Yanghua-Wang/dp/1405185406/ref=sr_1_1?ie=UTF8&s=books&qid=1268595741&sr=8-1#reader_1405185406 > > sends cold shivers down my spine. The author's premise seems > to be that there exists 'a' mathemathical model that influences > the Q factor of the trace. Then he goes on to list almost a > dozen different models for the effect (see the list of subchapters > in chapter 3). That alone sets off all the alarms in my mind. > > I used to do those kinds of things ages ago and my experience > is that the earth is a random medium in every sense of the > word. Unless you sample it directly - drill a hole and > dig stuff out of it - one does not know much. While any of > the proposed models might be defended in one setting, the > reality is that there are gazillion other situations in the > same survey where the model is invalid.Okay, thank you for your post, Rune. Nicholas

Reply by ●March 15, 20102010-03-15

On 14 Mar, 20:54, Rune Allnor <all...@tele.ntnu.no> wrote:> Just browsing the table of contents of the book, > > http://www.amazon.com/Seismic-Inverse-Filtering-Yanghua-Wang/dp/14051... > > sends cold shivers down my spine. The author's premise seems > to be that there exists 'a' mathemathical model that influences > the Q factor of the trace. Then he goes on to list almost a > dozen different models for the effect (see the list of subchapters > in chapter 3). That alone sets off all the alarms in my mind. > > I used to do those kinds of things ages ago and my experience > is that the earth is a random medium in every sense of the > word. Unless you sample it directly - drill a hole and > dig stuff out of it - one does not know much. While any of > the proposed models might be defended in one setting, the > reality is that there are gazillion other situations in the > same survey where the model is invalid.OK, maybe I should elaborate a bit on these things and why my spine goes cold. It is well-known that seismic waves travelling through the earth experience frequency-dependent attenuation. It's the same effect people hear in thunderstorms or near shooting ranges: Thunders or shots that are set off close to the listener are percievet as sharp 'snappish' bangs, while thunders or shots that are set off at a distance is percieved as a low rumbling. The difference is that the higher frequency bands are attenuated faster than the lower frequency bands, thus distorting the transient as a function of travelled distance. This effect has a huge impact on matched-filter processing in seismics: What are the chances of detectning the pulse waveform if the filter is set up to match the original emitted pulse, while the recieved pulse has undergone significant frequency-dependent attenuation? This is the question the constant Q algorithms attempt to answer. The problem is - as always - that one needs some sort of analytic model of this frequency-dependent attenuation in order to incorporate it in the processing. While the analytic model might be simple, the reality is not. Just about anything you will find in the real world will impose some sort of frequency-dependent response: - Grain & pore sizes in sedimentary rocks - frequency dependent response - Rough surfaces on boundaries between rocks - frequency dependent response - Micro-layered anisotropy in sedimentary rocks - frequency dependent response - Micro-cracks in rocks - frequency dependent response - Volume inhomogeneities in rocks - frequency dependent response - Fluid contents in pores - frequency-dependent response --- - Reflections off sequences of rock layers - frequency- dependent response - Conversions between wave types - frequency-dependent response So if one wants to start messing with these things, one has to be aware that *all* the factors influence *everything* *all* the time. As always, it's the one you don't see (or ignore) that will eventually take you down. All the items on the list above the '---' separator (and presumably a number of other items) are 'obvious' factors that affect the Q factor of the recieved pulse. Don't be surprised if you find a number of such factors discussed in the literature, with associated analytic or empirical models for the Q factor. As far as I am concerned, it is the latter two factors, reflections and conversions between waves, that are most likely to throw you off. These are not considered Q factors, but dominate the propagation path of the seismic energy. In other words, you will have to get those factors ~100% right before it makes sense to discuss the other, minor factors on the list. Again, I've messed with that sort of stuff in the past. I am not tempted to reacquaint myself with these things. Rune

Reply by ●March 15, 20102010-03-15

Rune Allnor wrote:> Again, I've messed with that sort of stuff in the past. > I am not tempted to reacquaint myself with these things.BTDT with electromagnetic problems :)))) But, what is the point in solving the problem if it is soluable?> > RuneVLV

Reply by ●March 15, 20102010-03-15

> > It is well-known that seismic waves travelling through the > earth experience frequency-dependent attenuation. It's the > same effect people hear in thunderstorms or near shooting > ranges: Thunders or shots that are set off close to the > listener are percievet as sharp 'snappish' bangs, while > thunders or shots that are set off at a distance is percieved > as a low rumbling.Yes - this is a good explanation of the physics. I couldn't have written it better myself.> > The difference is that the higher frequency bands are > attenuated faster than the lower frequency bands, thus > distorting the transient as a function of travelled > distance. > > This effect has a huge impact on matched-filter processing > in seismics: What are the chances of detectning the pulse > waveform if the filter is set up to match the original > emitted pulse, while the recieved pulse has undergone > significant frequency-dependent attenuation? > > This is the question the constant Q algorithms attempt to > answer. > > The problem is - as always - that one needs some sort of > analytic model of this frequency-dependent attenuation > in order to incorporate it in the processing. While the > analytic model might be simple, the reality is not. > Just about anything you will find in the real world will > impose some sort of frequency-dependent response: > > - Grain& pore sizes in sedimentary rocks - frequency > dependent response > - Rough surfaces on boundaries between rocks - frequency > dependent response > - Micro-layered anisotropy in sedimentary rocks - frequency > dependent response > - Micro-cracks in rocks - frequency dependent response > - Volume inhomogeneities in rocks - frequency dependent > response > - Fluid contents in pores - frequency-dependent response > --- > - Reflections off sequences of rock layers - frequency- > dependent response > - Conversions between wave types - frequency-dependent > response > > So if one wants to start messing with these things, one > has to be aware that *all* the factors influence *everything* > *all* the time. As always, it's the one you don't see > (or ignore) that will eventually take you down.Seismology (or the related field of non-destructive testing, NDT) can sometimes get very complicated. That's the reason why I do more research in NDT rather then seismology. IMHO, the distances over which measurements are taken are smaller and the physics is simpler. But even NDT poses a number of significant challenges. Nothing is ever really simple.> > All the items on the list above the '---' separator (and > presumably a number of other items) are 'obvious' factors > that affect the Q factor of the recieved pulse. Don't be > surprised if you find a number of such factors discussed > in the literature, with associated analytic or empirical > models for the Q factor. > > As far as I am concerned, it is the latter two factors, > reflections and conversions between waves, that are most > likely to throw you off. These are not considered Q factors, > but dominate the propagation path of the seismic energy. > In other words, you will have to get those factors ~100% > right before it makes sense to discuss the other, minor > factors on the list. >Thanks Rune-- Nicholas

Reply by ●March 15, 20102010-03-15

On 15 Mar, 15:33, Vladimir Vassilevsky <nos...@nowhere.com> wrote:> Rune Allnor wrote: > > Again, I've messed with that sort of stuff in the past. > > I am not tempted to reacquaint myself with these things. > > BTDT with electromagnetic problems :)))) > > But, what is the point in solving the problem if it is soluable?????? My impression is that a lot of people think that because one can express a chain of cause(s) + effect(s) that somehow explain a certain scenario, one can also 'undo' a number of destructive or unwanted effects. My favourite example to show why this is erratic thinking, is plain ol' Newtonian gravity: The formula is simple - it explains the effects of gravity - but one can not use it to remove gravity in the real world: - Aerospace systems will have to deal with weight, irrespective of the gravity formula. - Floating vessels will have to deal with stability issues irrespective of the gravity formula. - Building foundations will have to be dimensioned to the loads they are supposed to support, irrespective of the gravity formula. Don't get me wrong - the gravity formula is essential to describe each individual scenario, and is key to be able to dimension the systems correctly. The formula only allows people to *handle* the gravity; not *alter* it. But then - I'm merely an engineer who wants to make systems that actually work. "Making systems that actually work" is by no means the same as "getting an income". It is my impression that a lot of people go with these inverse methods because it is impossible to prove thay they *can't* work. A lacking result in this test can always be blamed on some missing or poorly handled detail. So it is always possible to obtain more funding. Prticularly if this is a long-running project that has already soaked immense amounts of $$$. Oh well. Rune