The Collaborative International Dictionary of English v.0.48:

Geostatic \Ge`o*stat"ic\, a. [Gr. ge`a, gh^, earth + E. static.]
   (Civil Engin.)
   Relating to the pressure exerted by earth or similar
   substance.
   [1913 Webster]

   Geostatic arch, an arch having a form adapted to sustain
      pressure similar to that exerted by earth. --Rankine.
      [1913 Webster]