def _compute_anelastic_attenuation_term(self, C, rrup, mag):
        """
        Compute magnitude-distance scaling term as defined in equation 21,
        page 2291 (Tavakoli and Pezeshk, 2005)
        """
        r = (rrup**2. + (C['c5'] * np.exp(C['c6'] * mag +
                                          C['c7'] * (8.5 - mag)**2.5))**2.)**.5
        f3 = ((C['c4'] + C['c13'] * mag) * np.log(r) +
              (C['c8'] + C['c12'] * mag) * r)
        return f3
Compute magnitude-distance scaling term as defined in equation 21,
        page 2291 (Tavakoli and Pezeshk, 2005)