code: def _compute_mean_on_rock(self, C, mag, rrup, rvol, hypo_depth, CN, CR,
                                f4HW):
          
  
          lnSA_AB = (
              # line 1 of equation 1
              C['c1'] + C['c4as'] * (mag - 6) +
              # line 2
              C['c3as'] * (8.5 - mag) ** 2 +
              # line 3
              C['c5'] * rrup +
              # line 3 and 4
              (C['c8'] + C['c6as'] * (mag - 6)) *
              np.log((rrup ** 2 + C['c10as'] ** 2) ** 0.5) +
              # line 5
              C['c46'] * rvol +
              # line 6
              C['c32'] * CN + C['c33as'] * CR + f4HW
          )
  
          return lnSA_AB
docs: Compute mean value on site class A/B (equation 1 on page 22)