code: def _compute_distance_scaling(self, C, mag, rrup):
          
          g = C['c5'] + C['c6'] * 0.5 + C['c7'] * 0.5
  
          return (
              rrup ** 2 +
              (np.exp(C['c8'] * mag + C['c9'] * (8.5 - mag) ** 2) * g) ** 2
          )
docs: Compute distance scaling term (eq.3, page 319).
  
          The distance scaling assumes the near-source effect of local site
          conditions due to 50% very firm soil and soft rock and 50% firm rock.