def _get_vs30star(self, vs30, imt):
        """
        This computes equations 8 and 9 at page 1034
        """
        # compute the v1 value (see eq. 9, page 1034)
        if imt.name == "SA":
            t = imt.period
            if t <= 0.50:
                v1 = 1500.0
            elif t < 3.0:
                v1 = np.exp(-0.35 * np.log(t / 0.5) + np.log(1500.))
            else:
                v1 = 800.0
        elif imt.name == "PGA":
            v1 = 1500.0
        else:
            # This covers the PGV case
            v1 = 1500.0
        # set the vs30 star value (see eq. 8, page 1034)
        vs30_star = np.ones_like(vs30) * vs30
        vs30_star[vs30 >= v1] = v1
        return vs30_star
This computes equations 8 and 9 at page 1034