code: def _compute_site_scaling(self, vs30, mean):
          
          site_factor = np.ones(len(vs30), dtype=float)
          idx = vs30 <= 360.
          site_factor[idx] = 1.4
          idx = vs30 > 760.0
          site_factor[idx] = 0.6
          return np.log(np.exp(mean) * site_factor)
docs: Scales the ground motions by increasing 40 % on NEHRP class D/E sites,
          and decreasing by 40 % on NEHRP class A/B sites