code: def get_site_amplification(self, C, sites):
          
          # Gets delta normalised z1
          dz1 = sites.z1pt0 - np.exp(self._get_lnmu_z1(sites.vs30))
          f_s = C["c5"] * dz1
          # Calculates site amplification term
          f_s[dz1 > self.CONSTANTS["dz1ref"]] = (C["c5"] *
                                                 self.CONSTANTS["dz1ref"])
          idx = sites.vs30 > self.CONSTANTS["v1"]
          f_s[idx] += (C["c4"] * np.log(self.CONSTANTS["v1"] / C["vref"]))
          idx = np.logical_not(idx)
          f_s[idx] += (C["c4"] * np.log(sites.vs30[idx] / C["vref"]))
          return f_s
docs: Returns the site amplification term