# [CIG-SEISMO] Help needed regarding SPECFEM2D

Dimitri Komatitsch dimitri.komatitsch at univ-pau.fr
Sat Oct 23 06:09:51 PDT 2010

```Dear Aqeel,

Yes, both are feasible (and easy to implement):

- to implement a force distributed along an edge, you need to implement
its 1D integral; what you can do is have a look at what we do to
implement the Stacey-Clayton-Enquist absorbing boundary conditions and
cut and paste one of the 1D edge integrals from there;
in the book of Tom Hughes (1987) you will also find a detailed
description of element edge integrals and edge loads (I do not remember
the page numbers, but I remember it is there somewhere):

@BOOK{Hug87,
title = {The finite element method, linear static and dynamic finite
element analysis},
publisher = {Prentice-Hall International},
year = {1987},
author = {Thomas J. R. Hughes},
address = {Englewood Cliffs, New Jersey, USA}}

- using an initial displacement field is easy, just set arrays
displ_elastic and veloc_elastic to something different from zero before
the time loop (you need two initial conditions for a second-order
hyperbolic system, thus you need to set velocity in addition to
displacement).

Best regards,
Dimitri.

On 10/19/2010 11:21 AM, Aqeel Chaudhry wrote:
> Dear all,
> I am using SPECFEM2D code. I need help to implement force which is not a point
> source but rather a force distributed along one edge. For example, I want to
> implement a Ricker wave on the whole bottom edge which travels only in upward
> direction (z-axis) and acts on the whole bottom edge instead of just one
> point. It is important for me that the component of force should be zero in
> x-direction in this case. Is it possible? If yes, which part of the code
> should I modify?
>
> Also, if the above is possible, then is it also possible to do the above by
> applying the source as an initial condition (displacement), not a force?
>
> Though I have been playing around with the code for past 2 months but still
> not able to figure out because I am not so good at it.
>
>
> Aqeel
> _______________________________________________
> CIG-SEISMO mailing list
> CIG-SEISMO at geodynamics.org
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>

--
Dimitri Komatitsch - dimitri.komatitsch aT univ-pau.fr
Professor, University of Pau, Institut universitaire de France,
CNRS and INRIA Magique3D, France   http://www.univ-pau.fr/~dkomati1
```