def _get_phi_al_regional(self, C, mag, vs30measured, rrup):
        """
        Returns intra-event (Phi) standard deviation (equation 24, page 1046)
        """
        phi_al = np.ones((len(vs30measured)))
        s1 = np.ones_like(phi_al) * C['s1e']
        s2 = np.ones_like(phi_al) * C['s2e']
        s1[vs30measured] = C['s1m']
        s2[vs30measured] = C['s2m']
        if mag < 4:
            phi_al *= s1
        elif mag <= 6:
            phi_al *= s1 + (s2 - s1) / 2. * (mag - 4.)
        else:
            phi_al *= s2
        return phi_al
Returns intra-event (Phi) standard deviation (equation 24, page 1046)