code: def _compute_large_distance_term(self, C, dists, rup):
          
          # equation 15, page 79
          if rup.mag < 5.5:
              T6 = 1.0
          elif rup.mag >= 5.5 and rup.mag <= 6.5:
              T6 = 0.5 * (6.5 - rup.mag) + 0.5
          else:
              T6 = 0.5
  
          # equation 14, page 79
          large_distance_term = np.zeros_like(dists.rrup)
          idx = dists.rrup >= 100.0
          large_distance_term[idx] = C['a18'] * (dists.rrup[idx] - 100.0) * T6
  
          return large_distance_term
docs: Compute and return large distance model term, that is the 8-th term
          in equation 1, page 74. The calculation of this term is explained in
          paragraph 'Large Distance Model', page 78.