code: def _construct_surface(lons, lats, upper_depth, lower_depth):
      
      depths = np.array([
          np.zeros_like(lons) + upper_depth,
          np.zeros_like(lats) + lower_depth
      ])
  
      mesh = RectangularMesh(
          np.tile(lons, (2, 1)), np.tile(lats, (2, 1)), depths
      )
      return SimpleFaultSurface(mesh)
docs: Utility method that constructs and return a simple fault surface with top
      edge specified by `lons` and `lats` and extending vertically from
      `upper_depth` to `lower_depth`.
  
      The underlying mesh is built by repeating the same coordinates
      (`lons` and `lats`) at the two specified depth levels.