SeisModels.jl
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What is SeisModels.jl?
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.
How to install
SeisModels.jl can be added to your Julia install like so:
julia> import Pkg; Pkg.add("SeisModels")
How to use
Model types
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.
Calculating properties
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:
- VP
- VS
- density ρ
- anisotropic parameters VPH, VPV, VSH, VSV 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)
Model input and output
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.
Reference
Exported types
SeisModel
: Abstract supertype of all modelsSeisModel1D
: Abstract supertype of 1D modelsLinearLayeredModel
: 1D model with linearly-varying properties between node pointsPREMPolyModel
: 1D model defined by PREM-style polynomials (of arbitrary degree)SteppedLayeredModel
: 1D model with constant properties between node points
Exported model instances
- Earth
AK135
IASP91
PREM
PREM_NOOCEAN
STW105
- Moon
MOON_WEBER_2011
Exported functions
Model properties
depth
: Return depth in km given a radius and modelhasattenuation
: Whether a model includes attenuationhasdensity
: Whether a model includes densityisanisotropic
: Whether a model is anisotropicradius
: Return radius in km given a depth and modelsurface_radius
: Radius in km of planet
Evaluation functions
evaluate
: Evaluate a given field for a model at any radiusvp
: P-wave velocity in km/svs
: S-wave velocity in km/sdensity
: Density in g/cm^3vph
: Horizontal P-wave velocity in km/svpv
: Vertical (radial) P-wave velocity in km/svsh
: Horizontally-polarised S-wave velocity in km/svsv
: Vertically-polarised S-wave velocity in km/seta
: Anisotropic parameterQμ
,Qmu
: Shear quality factorQκ
,Qkappa
: Bulk quality factor
Derived properties
bulk_modulus
: Bulk modulus (K) in Pagravity
: Acceleration due to gravity in m/s^2 at a given radiusmass
: Mass in kg from centre of model to a given radiusmoment_of_inertia
: MOI in kg m^2poissons_ratio
: Poisson's ratiopressure
: Pressure in Pashear_modulus
: Shear modulus (G) in Pasurface_mass
: Mass between two radiiyoungs_modulus
: Young's modulus in Pa
IO
read_mineos
: Read Mineos tabular-format filewrite_mineos
: Write Mineos tabular-format fileread_tvel
: Write tvel-format filewrite_tvel
: Write tvel-format file
Getting help
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]
Citing
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