code: def _get_stddevs(self, stddev_types, pgv):
          
          assert all(stddev_type in self.DEFINED_FOR_STANDARD_DEVIATION_TYPES
                     for stddev_type in stddev_types)
          std = np.zeros_like(pgv)
          std[pgv <= 25] = 0.20
          idx = (pgv > 25) & (pgv <= 50)
          std[idx] = 0.20 - 0.05 * (pgv[idx] - 25) / 25
          std[pgv > 50] = 0.15
          # convert from log10 to ln
          std = np.log(10 ** std)
          return [std for stddev_type in stddev_types]
docs: Return standard deviations as defined in equation 3.5.5-1 page 151