[WP] (i20_gremlin_example): provide discussion of layer.pdf

src/green/gremlin1/examples/Makefile

@@ -23,7 +23,7 @@ edit: flist; vim $<
 clean: ; 
 	-find . -name \*.bak | xargs --no-run-if-empty /bin/rm -v
 	-/bin/rm -vf flist
-	-/bin/rm *.inctex *.bak *.ps *.syg
+	-/bin/rm *.inctex *.bak *.ps *.syg *.pdf
 
 %.syg: %.mod.cfg zforce.src.cfg
 	syg $^ $@ -P 200,200,100.,3.
@@ -39,7 +39,7 @@ clean: ;
         -Y "phase-slowness / s km\u-1" \
         -S -A "normalized magnitude"
 
-2lay.ps: 2laysyg.ps 2lay.fig
-	fig2dev -L eps 2lay.fig $@
+layer.pdf: layersyg.ps layer.fig
+	fig2dev -L pdf layer.fig $@
 
 # ----- END OF Makefile ----- 

src/green/gremlin1/examples/README

@@ -3,4 +3,38 @@ this is <README>
 toy example for gremlin
 -----------------------
 
+============================================================================
+
+layer.pdf
+
+  Reproduces the layer-on-halfspace example by Forbriger (2001, Figure III.11
+  on page 88).
+
+  A: The fundamental mode at large frequency approaches asymptotically
+     a constant slowness which is slightly large than the shear-wave slowness of
+     the layer. At small frequency it approaches a value slightly larger than
+     the shear-wave slowness of the halfspace. The frequency at which the
+     transition from the layer's slowness to the half-space's slowness
+     appears, is controlled by the thickness of the layer.
+  B: The first higher mode. The non-dispersive sequences (horizontal tangent)
+     of the higher modes compose the direct and the refracted body waves by
+     interference. Horizontal tangents appear at the body-wave slowness of
+     layer and half-space.
+  C: Slowness of the direct shear-wave in the layer.
+  D: Slowness of the direct compressional wave in the layer.
+  E: Slowness of the refracted shear-wave from the half-space.
+  F: Slowness of the refracted compressional wave from the half-space.
+  G: Leaky-modes which effectively are multiple reflections within the layer.
+     The reflected wave interfere constructively, while radiating energy into
+     the half-space. Already modes between E and F loose energy by radiation
+     of shear-wave energy into the half-space and are, for this reason, not
+     members of the set of normal modes.
+
+============================================================================
+References
+----------
+
+  Forbriger, T., 2001. Inversion flachseismischer Wellenfeldspektren.
+    Dissertation. Universität Stuttgart. urn:nbn:de:bsz:93-opus-8610
+
 ----- END OF README ----- 

src/green/gremlin1/examples/2lay.fig → src/green/gremlin1/examples/layer.fig

@@ -8,7 +8,7 @@ Single
 -2
 1200 2
 2 5 0 1 0 -1 100 0 -1 0.000 0 0 -1 0 0 5
-	0 2laysyg.ps
+	0 layersyg.ps
 	 1035 1350 11830 1350 11830 8875 1035 8875 1035 1350
 2 1 1 3 0 7 100 0 -1 10.000 0 1 -1 0 0 2
 	 2700 3150 11925 3150