A Julia package for dealing with models of the Earth's (and other quasi-1D planets') seismic properties.

Currently, only three kinds of one-dimensional models are supported, but all model parameterisations and models are acceptable for inclusion. Contributions are welcome.

Built in models are listed in the documentation.

SeisModels.jl can be added to your Julia install like so:

`julia> import Pkg; Pkg.add("SeisModels")`

The module defines the SeisModel type and subtypes of this specify the kind of model (i.e., symmetry, nature of basis function, etc.).

```
julia> using SeisModels
julia> subtypes(SeisModel)
1-element Array{Any,1}:
SeisModel1D
julia> subtypes(SeisModel1D)
3-element Array{Any,1}:
LinearLayeredModel
PREMPolyModel
SteppedLayeredModel
```

So, there are currently three types of models implemented, all 1D models, with polynomial, linear or constant basis within each layer.

You can either create your own models by creating a new instance of one of the immutable types, or use the inbuilt models. For instance, for PREM, one can evaluate at an arbitrary radius:

*V*_{P}*V*_{S}- density
*ρ* - anisotropic parameters
*V*_{PH},*V*_{PV},*V*_{SH},*V*_{SV}and*η*

Calculate these by calling the function with the model as the first argument:

```
julia> vp(PREM, 3500)
13.71171655163979
julia> Qκ(PREM, 1000)
1327.7
julia> density(AK135, radius(AK135, 20))
2.449
```

In the last example, we used the `radius`

function to convert depth in the AK135 model
to radius and calculate the density at 20 km depth. Some functions also accept the
`depth`

keyword argument to instead evaluate properties at a point below the surface:

```
julia> density(AK135, radius(AK135, 20)) == density(AK135, 20, depth=true)
true
```

You can also evaluate values programmatically (i.e., where the parameter of
interest is a variable) by using the exported `evaluate`

function, and broadcast
the call to get multiple values:

```
julia> evaluate(AK135, :vp, 3580)
13.653094354838709
julia> parameters = (:vp, :vs, :density);
julia> evaluate.(AK135, parameters, 3680)
(13.591187999999999, 7.226264, 5.4003499999999995)
```

Support for reading and writing model files is currently limited. However, SeisModels
does support reading and writing of
Mineos-format ‘tabular’ models
(i.e., `SteppedLayeredModel`

s) via the `read_mineos`

and `write_mineos`

functions.

`SeisModel`

: Abstract supertype of all models`SeisModel1D`

: Abstract supertype of 1D models`LinearLayeredModel`

: 1D model with linearly-varying properties between node points`PREMPolyModel`

: 1D model defined by PREM-style polynomials (of arbitrary degree)`SteppedLayeredModel`

: 1D model with constant properties between node points

- Earth
`AK135`

`IASP91`

`PREM`

`PREM_NOOCEAN`

`STW105`

- Moon
`MOON_WEBER_2011`

`depth`

: Return depth in km given a radius and model`hasattenuation`

: Whether a model includes attenuation`hasdensity`

: Whether a model includes density`isanisotropic`

: Whether a model is anisotropic`radius`

: Return radius in km given a depth and model`surface_radius`

: Radius in km of planet

`evaluate`

: Evaluate a given field for a model at any radius`vp`

: P-wave velocity in km/s`vs`

: S-wave velocity in km/s`density`

: Density in g/cm^3`vph`

: Horizontal P-wave velocity in km/s`vpv`

: Vertical (radial) P-wave velocity in km/s`vsh`

: Horizontally-polarised S-wave velocity in km/s`vsv`

: Vertically-polarised S-wave velocity in km/s`eta`

: Anisotropic parameter`Qμ`

,`Qmu`

: Shear quality factor`Qκ`

,`Qkappa`

: Bulk quality factor

`bulk_modulus`

: Bulk modulus (*K*) in Pa`gravity`

: Acceleration due to gravity in m/s^2 at a given radius`mass`

: Mass in kg from centre of model to a given radius`moment_of_inertia`

: MOI in kg m^2`poissons_ratio`

: Poisson's ratio`pressure`

: Pressure in Pa`shear_modulus`

: Shear modulus (*G*) in Pa`surface_mass`

: Mass between two radii`youngs_modulus`

: Young's modulus in Pa

`read_mineos`

: Read Mineos tabular-format file`write_mineos`

: Write Mineos tabular-format file`read_tvel`

: Write tvel-format file`write_tvel`

: Write tvel-format file

Types and methods are documented, so at the REPL type `?`

to get a `help?>`

prompt, and type the name of the function:

```
help?> PREMPolyModel
search: PREMPolyModel
PREMPolyModel <: SeisModel1D
Type describing the Earth as a set of layers within which properties vary according to a set of
polynomials.
Physical parameters are represented by arrays of size (order+1,n), where n is the number of
layers, and order is the order of polynomial which is used to represent the parameter. Hence a
constant layer has size (1,n), and to compute the value of x in layer i, for an Earth radius of
a km, at a radius of r km, the expression is:
val_x = x[i,1] + (r/a)*x[i,2] + (r/a)^2*x[i,3] ... (r/a)^order*x[i,order+1]
```

If you use SeisModels.jl for your work, please cite the following paper:

- Nowacki, A., 2020. SeisModels.jl: A Julia package for models of the Earth’s interior. Journal of Open Source Software 5, 2043. doi:10.21105/joss.02043