def get_mean_and_stddevs(self, sites, rup, dists, imt, stddev_types):
        """
        Using a frequency dependent correction for the mean ground motion.
        Standard deviation is fixed.
        """
        mean, stddevs = super().get_mean_and_stddevs(sites, rup, dists,
                                                     imt, stddev_types)
        # Defining frequency
        if imt == PGA():
            freq = 50.0
        elif imt == PGV():
            freq = 2.0
        else:
            freq = 1./imt.period

        # Equation 3 of Atkinson (2010)
        x1 = np.min([-0.18+0.17*np.log10(freq), 0])

        # Equation 4 a-b-c of Atkinson (2010)
        if rup.hypo_depth < 20.0:
            x0 = np.max([0.217-0.321*np.log10(freq), 0])
        elif rup.hypo_depth > 35.0:
            x0 = np.min([0.263+0.0924*np.log10(freq), 0.35])
        else:
            x0 = 0.2

        # Limiting calculation distance to 1km
        # (as suggested by C. Bruce Worden)
        rjb = [d if d > 1 else 1 for d in dists.rjb]

        # Equation 2 and 5 of Atkinson (2010)
        mean += (x0 + x1*np.log10(rjb))/np.log10(np.e)

        return mean, stddevs
Using a frequency dependent correction for the mean ground motion.
        Standard deviation is fixed.