code: def _compute_vs30_star_factor(self, imt, vs30):
          
          v1 = self._compute_v1_factor(imt)
          vs30_star = vs30.copy()
          vs30_star[vs30_star >= v1] = v1
  
          return vs30_star, v1
docs: Compute and return vs30 star factor, equation 5, page 77.