code: def _compute_top_of_rupture_depth_term(self, C, rup):
          
          if rup.ztor >= 10.0:
              return C['a16']
          else:
              return C['a16'] * rup.ztor / 10.0
docs: Compute and return top of rupture depth term, that is the seventh term
          in equation 1, page 74. The calculation of this term is explained in
          paragraph 'Depth-to-Top of Rupture Model', page 78.