Use generic model parameters based on site class.

        Parameters
        ----------
        site_class: str
            Site classification. Possible options are:
             * Geomatrix AB
             * Geomatrix CD
             * USGS AB
             * USGS CD
             * USGS A
             * USGS B
             * USGS C
             * USGS D

            See the report for definitions of the Geomatrix site
            classication. USGS site classification is based on :math:`V_{s30}`:

            =========== =====================
            Site Class  :math:`V_{s30}` (m/s)
            =========== =====================
            A           >750 m/s
            B           360 to 750 m/s
            C           180 to 360 m/s
            D           <180 m/s
            =========== =====================

        Returns
        -------
        ToroVelocityVariation
            Initialized :class:`ToroVelocityVariation` with generic parameters.

def generic_model(cls, site_class, **kwds):
        """Use generic model parameters based on site class.

        Parameters
        ----------
        site_class: str
            Site classification. Possible options are:
             * Geomatrix AB
             * Geomatrix CD
             * USGS AB
             * USGS CD
             * USGS A
             * USGS B
             * USGS C
             * USGS D

            See the report for definitions of the Geomatrix site
            classication. USGS site classification is based on :math:`V_{s30}`:

            =========== =====================
            Site Class  :math:`V_{s30}` (m/s)
            =========== =====================
            A           >750 m/s
            B           360 to 750 m/s
            C           180 to 360 m/s
            D           <180 m/s
            =========== =====================

        Returns
        -------
        ToroVelocityVariation
            Initialized :class:`ToroVelocityVariation` with generic parameters.
        """
        p = dict(cls.PARAMS[site_class])
        p.update(kwds)
        return cls(**p)