code: def _apply_volcanic_front_correction(mean, x_vf, H, imt):
      
      V1 = np.zeros_like(x_vf)
      if imt.name == 'PGV':
          idx = x_vf <= 75
          V1[idx] = 4.28e-5 * x_vf[idx] * (H - 30)
          idx = x_vf > 75
          V1[idx] = 3.21e-3 * (H - 30)
          V1 = 10 ** V1
      else:
          idx = x_vf <= 75
          V1[idx] = 7.06e-5 * x_vf[idx] * (H - 30)
          idx = x_vf > 75
          V1[idx] = 5.30e-3 * (H - 30)
          V1 = 10 ** V1
      return np.log(np.exp(mean) * V1)
docs: Implement equation for volcanic front correction as described in equation
      3.5.2.-2, page 3-149 of "Technical Reports on National Seismic
      Hazard Maps for Japan"