code: def _compute_geometric_decay_term(self, C, mag, dists):
          
          c1 = self.CONSTS['c1']
          return (
              (C['b4'] + C['b5'] * (mag - c1)) *
              np.log(np.sqrt(dists.rjb ** 2.0 + C['b6'] ** 2.0))
          )
docs: Compute and return geometric decay term in equation 3,
          page 970.