# How to consider strike, and rake to green functions

**URL:** <https://community.geodynamics.org/t/how-to-consider-strike-and-rake-to-green-functions/3051>\
**Category:** PyLith\
**Created:** [July 27, 2023, 5:48pm UTC](https://community.geodynamics.org/t/how-to-consider-strike-and-rake-to-green-functions/3051 "2023-07-27T17:48:46Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![juanpamerino](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/juanpamerino/32/1346_2.png) [@juanpamerino](https://community.geodynamics.org/u/juanpamerino)\
**Post date:** [July 27, 2023, 5:48pm UTC](https://community.geodynamics.org/t/how-to-consider-strike-and-rake-to-green-functions/3051/1 "2023-07-27T17:48:46Z")

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Hello everyone,  
I calculated the green functions for the northern Chilean subduction zone in order to obtain the surface displacements for any slip model and compare it with GNSS observations.  
I got the following, where red arrows are my predictions and blue arrows are the observations (black are the residuals, the magnitude of the residuals arrow is wrong so ignore them):

 ![horizontal_carrasco](https://canada1.discourse-cdn.com/flex036/uploads/geodynamics/original/2X/8/8e33000c82776fbfe3b6e9368c659661befd314e.jpeg)

As you can see, the arrows of the residuals tend to have an orientation with respect to some angle, which suggests to me that strike or rake (or both) might be playing a role. To be honest I dont really know if there is a way to set the strike or rake in the step.cfg. So, is there a way to set the strike and rake at the moment of compute the green functions? or in order to consider this I have to rotate the GFs later?

Another question I have is how pylith delivers the green functions. If I take Okada’s formulation as a reference, I have to calculate the contributions of both strike-slip, dip-slip, and tensile, then the G matrix will have the form:

G = G\_ss + G\_ds + G\_ts

With this in mind, it is easy to assign strike, rake and dip to any sub-fault, but as far as I understood, what pylith gives me in this case is G right?. Is there a way to get G\_ss, G\_ds???

Here I upload you the files that im using for the simulation, Im using pylith 2.2.2.

[step07b.cfg](https://community.geodynamics.org/uploads/short-url/fwCNZxQRZ2yhAtYzBn3y5yFX8Y0.cfg) (4.5 KB)  
[pylithapp.cfg](https://community.geodynamics.org/uploads/short-url/cfrLLV1FUF9cuSODY6jgUN7JgyG.cfg) (6.7 KB)  
[greensfns.cfg](https://community.geodynamics.org/uploads/short-url/oI7N1DJAbTwZZCdhADqv0xQBIUq.cfg) (2.2 KB)

Here I show you the mesh I am using. I tried to make it as realistic as possible, considering topography, bathymetry, slab 2.0, a realistic moho  
geometry and a detailed tomography for the elastic properties of the crust.

 ![mesh_sized](https://canada1.discourse-cdn.com/flex036/uploads/geodynamics/original/2X/6/60bef3213239b13c13007c52c4dd1120c755d7f8.png)

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<div class="post-metadata">

**Author:** ![baagaard](https://yyz2.discourse-cdn.com/flex036/user_avatar/community.geodynamics.org/baagaard/32/615_2.png) [@baagaard](https://community.geodynamics.org/u/baagaard)\
**Post date:** [July 27, 2023, 6:17pm UTC](https://community.geodynamics.org/t/how-to-consider-strike-and-rake-to-green-functions/3051/2 "2023-07-27T18:17:56Z")

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In `step07b.cfg` you set the impulse\_dof to [1], which means PyLith is computing the Green’s functions only for the reverse component of slip.

```auto
[pylithapp.problem.interfaces.slab]
# Impulses for reverse slip.
# Note that it is possible to apply both left-lateral and updip slip
# (impulse_dof = [0,1]), but we separate the impulses into two problems.
impulse_dof = [1]

```

In the subduction-3d example, we use `step07a.cfg` to compute the Green’s functions for the left-lateral component. See the subduction-3d example for how to make use of both the left-lateral and reverse components in an inversion.