anchor.diff:  C----
   C Coordinates on fault plane (x,p,q) and distance from edges (ksi,eta)
   C----
  -      ksi(1) = x+len/2.0d0
  -      ksi(2) = x-len/2.0d0
  +      ksi(1) = x+len*0.5d0
  +      ksi(2) = x-len*0.5d0
   C      ksi(1) = x
   C      ksi(2) = x-len
         if (dabs(ksi(1)).lt.eps) ksi(1) = zro
  
positive.code: C----
  C Coordinates on fault plane (x,p,q) and distance from edges (ksi,eta)
  C----
        ksi(1) = x+len/2.0d0
        ksi(2) = x-len/2.0d0
  C      ksi(1) = x
  C      ksi(2) = x-len
        if (dabs(ksi(1)).lt.eps) ksi(1) = zro
  
negative.code:       COMMON /TAG/ thru
  
        if (thru.eq.0) then
        f(1,1) = TH*0.5d0    + CA2*ksi*q*Y11
        f(2,1) =               CA2*q/R
        f(3,1) = CA1*logRe   - CA2*q*q*Y11
        f(4,1) =               CA2*q/R
        f(5,1) = TH*0.5d0    + CA2*eta*q*X11
        f(6,1) = CA1*logRk   - CA2*q*q*X11
  
        f(1,2) = -ksi*q*Y11 - TH - CB*I1*sd
  