[CIG-SEISMO] Negative Jacobian in specfem2d

[Jami Johnson]

Hello,
I have created a very dense mesh with Gmsh, and when I check for the values
of the Jacobian in Gmsh they are all positive.  However, when I run it in
specfem2d, an error is thrown due to a negative Jacobian.  It seems to be a
very small percentage of my elements causing a problem.  I believe all of
my line loops are oriented correctly.  Are there any other potential causes
of a negative Jacobian?

Error in specfem2d:
--------------------------
 2  elements have a negative Jacobian, out of      1313871

geo file:
-----------
lc=0.00003;
xmax=0.015;
xmin=0.0;
ymin=-0.015;
ymax=0.0;
Point(1) = {xmax,ymax , 0, lc};
Point(2) = {xmax, ymin, 0, lc};
Point(3) = {xmin, ymin, 0, lc};
Point(4) = {xmin, ymax, 0, lc};
Line(1) = {1, 4};
Line(2) = {4, 3};
Line(3) = {3, 2};
Line(4) = {2, 1};
R=0.00025;
Centx=0.0075;
Centy=-0.005;
Point(5) = {Centx, R+Centy, 0, lc};
Point(6) = {R+Centx, Centy, 0, lc};
Point(7) = {-R+Centx, Centy, 0, lc};
Point(8) = {Centx, -R+Centy, 0, lc};
Point(9) = {Centx, Centy, 0, lc};
Circle(5) = {5, 9, 7};
Circle(6) = {7, 9, 8};
Circle(7) = {8, 9, 6};
Circle(8) = {6, 9, 5};
Line Loop(9) = {5, 6, 7, 8};
Line Loop(10) = {1, 2, 3, 4};

Plane Surface(10) = {10, 9};
Plane Surface(11) = {9};

Recombine Surface{10,11};
Mesh.SubdivisionAlgorithm=1;
Physical Line("Top") = {1};
Physical Line("Left") = {2};
Physical Line("Bottom") = {3};
Physical Line("Right") = {4};
Physical Surface("M1") = {10};
Physical Surface("M2") = {11};
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