code: def _get_site_type_dummy_variables(self, sites):
          
          S = np.zeros_like(sites.vs30)
          # S=0 for rock sites, S=1 otherwise pag 1.
          idxS = (sites.vs30 < 760.0)
          S[idxS] = 1
          return S
docs: Get site type dummy variables, ``S`` (for rock and soil sites)