convert velocities to moduli
    mainly to support Burnman operations

    :param rho: density in kg/m^3
    :param v_phi: bulk sound speed in m/s
    :param v_s: shear velocity in m/s
    :return: K_s and G

def velocities_to_moduli(rho, v_phi, v_s):
    """
    convert velocities to moduli
    mainly to support Burnman operations

    :param rho: density in kg/m^3
    :param v_phi: bulk sound speed in m/s
    :param v_s: shear velocity in m/s
    :return: K_s and G
    """
    return v_phi * v_phi * rho, v_s * v_s * rho