code: def _compute_soil_amplification(cls, C, vs30, pga_rock, imt):
          
          Sbc, Sc, Sd, Se = cls._compute_site_class_dummy_variables(vs30)
          sl = cls._compute_soil_linear_factor(pga_rock, imt)
  
          return (
              C['c5'] * sl * Sbc * 0.5 +
              C['c5'] * sl * Sc +
              C['c6'] * sl * Sd +
              C['c7'] * sl * Se
          )
docs: Compute soil amplification (5th, 6th, and 7th terms in equation 1,
          page 1706) and add the B/C site condition as implemented by NSHMP.