code: def _get_ln_a_n_max(self, C, n_sites, idx, rup):
          
          ln_a_n_max = C["lnSC1AM"] * np.ones(n_sites)
          for i in [2, 3, 4]:
              if np.any(idx[i]):
                  ln_a_n_max[idx[i]] += C["S{:g}".format(i)]
          return ln_a_n_max
docs: Defines the rock site amplification defined in equations 10a and 10b