@classmethod
def _compute_soil_amplification(cls, C, vs30, pga_rock, imt):
    """
        Compute soil amplification (5th, 6th, and 7th terms in equation 1,
        page 1706).
        """
    Sc, Sd, Se = cls._compute_site_class_dummy_variables(vs30)
    sl = cls._compute_soil_linear_factor(pga_rock, imt)
    return C['c5'] * sl * Sc + C['c6'] * sl * Sd + C['c7'] * sl * Se
