code: def _compute_v1_factor(self, imt):
          
          if imt.name == "SA":
              t = imt.period
              if t <= 0.50:
                  v1 = 1500.0
              elif t > 0.50 and t <= 1.0:
                  v1 = np.exp(8.0 - 0.795 * np.log(t / 0.21))
              elif t > 1.0 and t < 2.0:
                  v1 = np.exp(6.76 - 0.297 * np.log(t))
              else:
                  v1 = 700.0
          elif imt.name == "PGA":
              v1 = 1500.0
          else:
              # this is for PGV
              v1 = 862.0
  
          return v1
docs: Compute and return v1 factor, equation 6, page 77.