Greg
You have most of the answers in other e-mails, but none say that what the
colors mean in tomography is pertubations from a reference velocity model
that changes with depth. The color scale, which is given in %, is the
variation from that reference model.
If you want to play with the relations between seismic velocities,
density, temperature, pressure and rocks that you design yourself, then
there is a great Exel spreadsheet on the webpage of Bradley Hacker called
"Physprops" that is free. You design the rocks from mineral end members
(e.g., modal garnet with the percent almandine etc. in garnet plus the
same for pyroxene and so on), set the T and P and the program will give
you Vp, Vs and density that has been calculated using a number of
different methods (i.e. Voight-Reus-Hill and so on). There is a table with
the physical properties, shear modulos etc. that it uses to do this. If
you want, I have added a bit that calculates the major element composition
(in Wt.%) of the rock you make that I can give you as well.
There is a page with examples of rocks, so this spread sheet is very easy
to use and you can learn a lot.
Cheers
Dennis
> Dear Greg
> See www.mantleplumes.org, there are several discussions and opinions in
> the section “seismology”, also about the “red = hot, blue = cold” your
> students ask
>
>
>> Awesome answer! Thank you, Ernie! That is just what I was looking for!
>>
>> Best regards,
>> Greg
>>
>> On 3/17/2011 11:58 AM, Ernest Rutter wrote:
>>> It is a fact that velocity increases with the density of a suite of
>>> (different) rocks, but for constant elasticity velocity decreases with
>>> density. It is just that going from say, granite to peridotite, the
>>> increase in density is more than offset by the increase in stiffness.
>>> Denser rocks tend to be stiffer. Hotter rocks have lower densities AND
>>> lower stiffnesses. Stiffness is a much more variable property than
>>> density, so you can have denser rocks being faster than less dense
>>> rocks.
>>>
>>> Ernie Rutter
>>>
>>> -----Original Message-----
>>> From: Tectonics& structural geology discussion list
>>> [mailto:[log in to unmask]] On Behalf Of Gregory Dumond
>>> Sent: 17 March 2011 16:45
>>> To: [log in to unmask]
>>> Subject: P-wave velocity, Density, and Modulus
>>>
>>> There is a lot of remarkable work being done in North America, Tibet,
>>> and all over the globe using seismic tomography! Consequently, I
>>> receive
>>> questions from many students that are similar to "What do the red and
>>> blue colors mean?!"
>>>
>>> I first admit my unfortunate lack of anything but a basic education in
>>> geophysics. In my non-expert opinion, the equation for P-wave velocity
>>> (e.g., in Fowler (2005-2nd ed. on p. 102) appears at first to be
>>> nonintuitive, based on the following:
>>>
>>> (1) Classic experiments by Christensen and Mooney (1995: JGR-Solid
>>> Earth) and others demonstrate a general trend of P-wave velocity
>>> increase with increasing density. One of my illustrations for students
>>> is to hand them similarly-sized hand samples of basalt and eclogite to
>>> convey to them a sense of how phase changes and densification can occur
>>> in a fixed bulk composition. Coincidentally, the average P-wave
>>> velocity
>>> and density for mafic eclogite (7.984 km/s for a density of 3515 kg/m3)
>>> is greater than basalt (5.873 km/s for a density of 2926 kg/km3), at
>>> 762C and 50-km-depths (Christensen and Mooney, 1995).
>>>
>>> (2) The density term is in the denominator of the P-wave velocity
>>> equation, implying that density is (by definition) inversely
>>> proportional with seismic velocity. Yet, Birch's Law tells us that
>>> denser rocks DO have higher seismic velocities. This inspired me to
>>> look
>>> for references that have plotted Modulus as a function of Density. Web
>>> of Science provided few results. The most intriguing one involve a 2007
>>> publication in Nature Materials on the direct relationship between
>>> modulus and density in bone and some nanomaterials (Fan et al., 2007).
>>>
>>> I really like Professor Fowler's explanations on pp. 102-104 in her
>>> awesome "The Solid Earth..." textbook, but I have still encountered
>>> difficulties with regards to getting junior-senior undergraduate
>>> students (and some colleagues) to fully understand these relationships.
>>>
>>> I would sincerely appreciate any advice or guidance on this topic.
>>>
>>> With warmest regards,
>>> Gregory Dumond
>>> Department of Geosciences
>>> University of Arkansas, USA
>>
>> --
>> Gregory Dumond
>> Assistant Professor
>> Department of Geosciences
>> University of Arkansas
>> 18 Ozark Hall
>> Fayetteville, AR 72701
>> Phone: 479.575.3411
>> Email: [log in to unmask]
>> Web: http://geosciences.uark.edu/3858.php
>>
>> --
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>
>
> Rubén Somoza
> Dpto. Ciencias Geológicas, FCEyN, UBA
> Ciudad Universitaria, Pabellón 2
> C1428EHA, Buenos Aires, Argentina
>
>
> --
> Este mensaje ha sido analizado por MailScanner
> en busca de virus y otros contenidos peligrosos,
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