code: def _apply_amplification_factor(self, mean, vs30):
          
          assert np.all(vs30 == vs30[0])
          if abs(vs30[0]-600.) < 1e-10:
              return mean * np.log(10)
          elif abs(vs30[0]-400.) < 1e-10:
              return mean * np.log(10) + np.log(self.AMP_F)
          elif abs(vs30[0]-800.) < 1e-10:
              return mean * np.log(10) - np.log(1.25)
          else:
              raise ValueError('Si and Midorikawa 1999 do not support this Vs30 value')
docs: Apply amplification factor to scale PGV value from 600 to 400 m/s vs30
          and convert mean from base 10 to base e.
  
          The scaling factor from 600 m/s to 400 m/s was defined by NIED.
  
          The scaling factor from 600 m/s to 800m/s is valid just for the elastic
          case as no adjustment for kappa was considered.