def _compute_mean(self, C, rup, rjb):
        """
        Compute mean value according to equation 30, page 1021.
        """
        mean = (C['c1'] +
                self._compute_magnitude_term(C, rup) +
                self._compute_distance_term(C, rup, rjb))
        return mean
Compute mean value according to equation 30, page 1021.