def _get_stddevs(self, C, stddev_types, rup, imt, num_sites):
        """
        Return standard deviations as defined in eq. 4 and 5, page 744,
        based on table 8, page 744.
        Eq. 5 yields std dev in natural log, so convert to log10
        """
        stddevs = []
        for stddev_type in stddev_types:
            sigma_mean = self._compute_standard_dev(rup, imt, C)
            sigma_tot = np.sqrt((sigma_mean ** 2) + (C['SigmaReg'] ** 2))
            sigma_tot = np.log10(np.exp(sigma_tot))
            stddevs.append(sigma_tot + np.zeros(num_sites))
        return stddevs
Return standard deviations as defined in eq. 4 and 5, page 744,
        based on table 8, page 744.
        Eq. 5 yields std dev in natural log, so convert to log10