code: def _get_site_classification(self, vs30):
          
          site_class = np.ones(vs30.shape, dtype=int)
          idx = {}
          idx[1] = vs30 > 600.
          idx[2] = np.logical_and(vs30 > 300., vs30 <= 600.)
          idx[3] = np.logical_and(vs30 > 200., vs30 <= 300.)
          idx[4] = vs30 <= 200.
          for i in [2, 3, 4]:
              site_class[idx[i]] = i
          return site_class, idx
docs: Define the site class categories based on Vs30. Returns a
          vector of site class values and a dictionary containing logical
          vectors for each of the site classes