code: def _compute_intra_event_std(self, C, C_PGA, pga1100, mag, vs30,
                                   vs30measured):
          
          sigma_b = self._compute_sigma_b(C, mag, vs30measured)
          sigma_b_pga = self._compute_sigma_b(C_PGA, mag, vs30measured)
          delta_amp = self._compute_partial_derivative_site_amp(C, pga1100, vs30)
  
          std_intra = np.sqrt(sigma_b ** 2 + self.CONSTS['sigma_amp'] ** 2 +
                              (delta_amp ** 2) * (sigma_b_pga ** 2) +
                              2 * delta_amp * sigma_b * sigma_b_pga * C['rho'])
  
          return std_intra
docs: Compute intra event standard deviation (equation 24) as described
          in the errata and not in the original paper.