<p>There are several published models of Earth’s 3-D mass density distribution, based variously on (1) relationships (often empirical) between seismic wave speed and density, (2) gravity observations and (3) geodynamical modelling. However, these models generally have low resolution (they only show smooth, large-scale variations) and may not agree with one another. One example is SP12RTS.</p>

CC BY-SA 4.0
2024-11-27T17:23:42.043Z
2024-11-27T17:23:42.043Z
Harry Kuril
<p>Here's an extensive list of Earth models, many of which are anisotropic. You'll probably want to focus on tomographic models rather than reference models.</p>
<p><a href="http://ds.iris.edu/spud/earthmodel" rel="nofollow noreferrer">http://ds.iris.edu/spud/earthmodel</a></p>

CC BY-SA 4.0
2021-05-08T11:00:12.323Z
That's a nice resource but does any of these models include mass density distributions? I only see seismic velocity measurements and I want the mass distribution.
Swike
CC BY-SA 4.0
2021-05-08T21:12:34.677Z
Unfortunately, many seismic models don't explicitly provide density. PREM is very convenient in that it gives you a bunch of quantities. Of course, density can easily be calculated from seismic velocities if you have estimates for shear and/or bulk moduli.
g.z.
CC BY-SA 4.0
2021-05-12T15:04:00.440Z
How should I proced then? Should I wait a few weeks for someone to show a density model or is it probably not found anywhere? Should I calculate it? How?
Swike
CC BY-SA 4.0
2021-05-12T21:10:32.183Z
Waiting probably won't be helpful.

I don't know what you're trying to do, so it's kind of hard to give advice on how you should proceed. Why isn't the PREM density profile suitable for what you're trying to do?
g.z.
CC BY-SA 4.0
2021-05-15T21:33:31.000Z
I want to calculate free-fall paths through Earth's interior. I first did it with PREM but I now want to make a second order approximation, one that implies the non-symetric distribution of matter in Earth's interior to see what trajectories are possible and other curiosities (like what is the antipodal shortest travel time in the true Earth). That's why I need a more realistic model than PREM, because my goal is to adress a physics example with varying degrees of accuracy to show how complexity makes for devils in the details.
Swike
CC BY-SA 4.0
2021-05-15T22:29:29.950Z
One thing you could do is get an approximation for the shear modulus as a function of depth or pressure, and then use the S-wave velocity from one of the models to calculate density. I can't remember if PREM gives shear modulus as a function of depth, but it's worth checking. Some of the other models in the link I gave might provide it as well. Also, if you're at all familiar with Python, I recommend taking a look at https://burnman.org/. You can build a model of Earth and calculate seismic profiles. You can play around with the mineralogy and see how that changes different properties.
g.z.
CC BY-SA 4.0
2021-05-07T19:44:59.357Z
2021-05-07T19:44:59.357Z
g.z.
<p>So, I just discovered <a href="https://en.wikipedia.org/wiki/Preliminary_reference_Earth_model" rel="noreferrer">PREM (the Preliminary reference Earth model)</a> which models the density distribution of matter inside the Earth to any depth.</p>
<p>The PREM is very convenient but since it only depends on the depth I see that is an isotropic model, meaning that it deoesn't matter from which surface coordinates we are digging, it only accounts for radial variations in density from the core. I know that Earth's interior is not distributed in perfect spherical symmetry since there are things like <a href="https://en.wikipedia.org/wiki/Large_low-shear-velocity_provinces" rel="noreferrer">Large low-shear velocity provinces</a> and giant <a href="https://science.sciencemag.org/content/363/6428/736" rel="noreferrer">slabs of solid crust floating in the mantle</a> revealed by <a href="http://dagik.org/misc/gst/GAP_P4/index.html" rel="noreferrer">seismic tomography</a>, and <a href="https://en.wikipedia.org/wiki/Gravity_anomaly" rel="noreferrer">gravitational anomalies</a>.</p>
<p>I was wondering if there is a much more accurate model for the density distribution of Earth that accounts for the aforementioned asymmetries, and where can I download that data?</p>

CC BY-SA 4.0
2024-11-27T17:12:25.650Z
Just a note on terminology, in seismology, 'anisotropic' typically refers to materials where the seismic wave speed is different depending on the direction of wave propagation. Based on your question, you are asking for 'non-spherically symmetric' models. Incidentally PREM is spherically symmetric but not isotropic. In parts of the mantle, it has wave speeds that differ in the upwards and horizontal directions.
Harry Kuril
CC BY-SA 4.0
2024-11-28T12:53:47.093Z
@HarryKuril Thanks for the correction, this is a mistake I made because my background is in physics.
Swike
<geophysics><seismology>
Where can I find an anisotropic PREM-like model for Earth's interior?
Swike
# Where can I find an anisotropic PREM-like model for Earth's interior?

(Asked by: username_0 on 2021-04-04)

So, I just discovered [PREM (the Preliminary reference Earth model)](https://en.wikipedia.org/wiki/Preliminary_reference_Earth_model) which models the density distribution of matter inside the Earth to any depth.

The PREM is very convenient but since it only depends on the depth I see that is an isotropic model, meaning that it deoesn't matter from which surface coordinates we are digging, it only accounts for radial variations in density from the core. I know that Earth's interior is not distributed in perfect spherical symmetry since there are things like [Large low-shear velocity provinces](https://en.wikipedia.org/wiki/Large_low-shear-velocity_provinces) and giant [slabs of solid crust floating in the mantle](https://science.sciencemag.org/content/363/6428/736) revealed by [seismic tomography](http://dagik.org/misc/gst/GAP_P4/index.html), and [gravitational anomalies](https://en.wikipedia.org/wiki/Gravity_anomaly).

I was wondering if there is a much more accurate model for the density distribution of Earth that accounts for the aforementioned asymmetries, and where can I download that data?

**Tags:** geophysics, seismology

> **Comments:**
> **username_1**: Just a note on terminology, in seismology, 'anisotropic' typically refers to materials where the seismic wave speed is different depending on the direction of wave propagation. Based on your question, you are asking for 'non-spherically symmetric' models. Incidentally PREM is spherically symmetric but not isotropic. In parts of the mantle, it has wave speeds that differ in the upwards and horizontal directions.  
> **username_0**: @username_1 Thanks for the correction, this is a mistake I made because my background is in physics.  

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## 2 answers

### Answer by username_1 on 2024-11-27. Score: 2

There are several published models of Earth’s 3-D mass density distribution, based variously on (1) relationships (often empirical) between seismic wave speed and density, (2) gravity observations and (3) geodynamical modelling. However, these models generally have low resolution (they only show smooth, large-scale variations) and may not agree with one another. One example is SP12RTS.


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### Answer by username_2 on 2021-05-07. Score: 0

Here's an extensive list of Earth models, many of which are anisotropic. You'll probably want to focus on tomographic models rather than reference models.

<http://ds.iris.edu/spud/earthmodel>

> **Comments:**
> **username_0**: That's a nice resource but does any of these models include mass density distributions? I only see seismic velocity measurements and I want the mass distribution.  
> **username_2**: Unfortunately, many seismic models don't explicitly provide density. PREM is very convenient in that it gives you a bunch of quantities. Of course, density can easily be calculated from seismic velocities if you have estimates for shear and/or bulk moduli.  
> **username_0**: How should I proced then? Should I wait a few weeks for someone to show a density model or is it probably not found anywhere? Should I calculate it? How?  
> **username_2**: Waiting probably won't be helpful.  I don't know what you're trying to do, so it's kind of hard to give advice on how you should proceed. Why isn't the PREM density profile suitable for what you're trying to do?  
> **username_0**: I want to calculate free-fall paths through Earth's interior. I first did it with PREM but I now want to make a second order approximation, one that implies the non-symetric distribution of matter in Earth's interior to see what trajectories are possible and other curiosities (like what is the antipodal shortest travel time in the true Earth). That's why I need a more realistic model than PREM, because my goal is to adress a physics example with varying degrees of accuracy to show how complexity makes for devils in the details.  
> **username_2**: One thing you could do is get an approximation for the shear modulus as a function of depth or pressure, and then use the S-wave velocity from one of the models to calculate density. I can't remember if PREM gives shear modulus as a function of depth, but it's worth checking. Some of the other models in the link I gave might provide it as well. Also, if you're at all familiar with Python, I recommend taking a look at https://burnman.org/. You can build a model of Earth and calculate seismic profiles. You can play around with the mineralogy and see how that changes different properties.  

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