[cig-commits] r19316 - in seismo/2D/SPECFEM2D/trunk: EXAMPLES/attenuation src/specfem2D

[dkomati1 at geodynamics.org]

Author: dkomati1
Date: 2011-12-27 15:12:43 -0800 (Tue, 27 Dec 2011)
New Revision: 19316

Modified:
   seismo/2D/SPECFEM2D/trunk/EXAMPLES/attenuation/README
   seismo/2D/SPECFEM2D/trunk/src/specfem2D/attenuation_model.f90
Log:
fixed a comment in the attenuation routine, and added more details about how to use EXAMPLES/attenuation


Modified: seismo/2D/SPECFEM2D/trunk/EXAMPLES/attenuation/README
===================================================================
--- seismo/2D/SPECFEM2D/trunk/EXAMPLES/attenuation/README	2011-12-27 22:58:22 UTC (rev 19315)
+++ seismo/2D/SPECFEM2D/trunk/EXAMPLES/attenuation/README	2011-12-27 23:12:43 UTC (rev 19316)
@@ -19,8 +19,25 @@
 4. execute script to run mesher and solver for the PSV case:
    ./process.sh
 
-5. check out the output files in the local directory OUTPUT_FILES; in particular, you can type "gnuplot plot_compare_to_analytical_solution.gnu" to compare the seismograms computed to the quasi-analytical solution of Carcione et al. (1988). Note that because our example has no absorbing conditions on the edges of the grid, there are extra (spurious) waves after the main P and S waves, reflected off the edges of the grid, which are not present in the quasi-analytical solution and which you can safely ignore. Beware that the reference solution is not exact, only quasi-exact (i.e., the formulation uses an approximation, and some integrals are computed numerically) therefore some small discrepancies can be noticed.
+5. check out the output files in the local directory OUTPUT_FILES; in particular, you can type "gnuplot plot_compare_to_analytical_solution.gnu" to compare the seismograms computed to the quasi-analytical solution of Carcione et al. (1988). 
 
+Note that because our example has no absorbing conditions on the edges of the grid, there are extra (spurious) waves after the main P and S waves, reflected off the edges of the grid, which are not present in the quasi-analytical solution and which you can safely ignore.
+
+Beware that the reference solution is not exact, only quasi-exact (i.e., the formulation uses an approximation, and some integrals are computed numerically) therefore some small discrepancies can be noticed.
+
+More importantly, in the example provided, "tau" relaxation times for attenuation memory variables are recomputed using approximate quality factor targets of Qkappa approximately equal to 27 and Qmu / Qs approximately equal to 20, read (roughly) from Figure 1 page 604 of the article of Carcione et al. (1988). This will NOT lead to the exact same "tau" values as in Table 1 of Carcione et al. (1988). Thus, in order to perform a far more precise comparison to the analytical solution, which is computed using the "tau" values from Table 1 of Carcione et al. (1988), in file "src/specfem2D/attenuation_model.f90" you should impose this instead for this test (only):
+
+  tau_epsilon_nu1(1) = 0.0325305d0
+  tau_sigma_nu1(1)   = 0.0311465d0
+  tau_epsilon_nu2(1) = 0.0332577d0
+  tau_sigma_nu2(1)   = 0.0304655d0
+
+  tau_epsilon_nu1(2) = 0.0032530d0
+  tau_sigma_nu1(2)   = 0.0031146d0
+  tau_epsilon_nu2(2) = 0.0033257d0
+  tau_sigma_nu2(2)   = 0.0030465d0
+
+
 References:
 -----------
 

Modified: seismo/2D/SPECFEM2D/trunk/src/specfem2D/attenuation_model.f90
===================================================================
--- seismo/2D/SPECFEM2D/trunk/src/specfem2D/attenuation_model.f90	2011-12-27 22:58:22 UTC (rev 19315)
+++ seismo/2D/SPECFEM2D/trunk/src/specfem2D/attenuation_model.f90	2011-12-27 23:12:43 UTC (rev 19316)
@@ -84,7 +84,7 @@
 ! from J. M. Carcione, Seismic modeling in viscoelastic media, Geophysics,
 ! vol. 58(1), p. 110-120 (1993) for two memory-variable mechanisms (page 112).
 ! Beware: these values implement specific values of the quality factors:
-! Qp approximately equal to 13 and Qs approximately equal to 10,
+! Qp approximately equal to 13, Qkappa approximately to 20 and Qmu / Qs approximately to 10,
 ! which means very high attenuation, see that paper for details.
 ! tau_epsilon_nu1(1) = 0.0334d0
 ! tau_sigma_nu1(1)   = 0.0303d0
@@ -100,7 +100,7 @@
 ! in a linear viscoelastic medium, Geophysical Journal International,
 ! vol. 95, p. 597-611 (1988) for two memory-variable mechanisms (page 604).
 ! Beware: these values implement specific values of the quality factors:
-! Qp approximately equal to 27 and Qs approximately equal to 20,
+! Qkappa approximately to 27 and Qmu / Qs approximately to 20,
 ! which means very high attenuation, see that paper for details.
 !  tau_epsilon_nu1(1) = 0.0325305d0
 !  tau_sigma_nu1(1)   = 0.0311465d0