[cig-commits] r11920 - seismo/3D/SPECFEM3D/trunk

[dkomati1 at geodynamics.org]

Author: dkomati1
Date: 2008-05-06 13:54:35 -0700 (Tue, 06 May 2008)
New Revision: 11920

Modified:
   seismo/3D/SPECFEM3D/trunk/specfem3D.f90
Log:
added comment about attenuation for P waves (Q_\alpha)


Modified: seismo/3D/SPECFEM3D/trunk/specfem3D.f90
===================================================================
--- seismo/3D/SPECFEM3D/trunk/specfem3D.f90	2008-05-06 20:53:20 UTC (rev 11919)
+++ seismo/3D/SPECFEM3D/trunk/specfem3D.f90	2008-05-06 20:54:35 UTC (rev 11920)
@@ -2051,6 +2051,12 @@
   R_yy(i,j,k,ispec,i_sls) = alphaval_loc * R_yy(i,j,k,ispec,i_sls) + betaval_loc * Sn + gammaval_loc * Snp1
 
 ! term in zz not computed since zero trace
+! This is because we only implement Q_\mu attenuation and not Q_\Kappa.
+! Note that this does *NOT* imply that there is no attenuation for P waves
+! because for Q_\Kappa = infinity one gets (see for instance Dahlen and Tromp (1998)
+! equation (9.59) page 350): Q_\alpha = Q_\mu * 3 * (V_p/V_s)^2 / 4
+! therefore Q_\alpha is not zero; for instance for V_p / V_s = sqrt(3)
+! we get Q_\alpha = (9 / 4) * Q_\mu = 2.25 * Q_\mu
 
 ! term in xy
   Sn   = factor_loc * epsilondev_xy(i,j,k,ispec)