code: def _get_stddevs(self, stddev_types, rrup):
          
          assert all(stddev_type in self.DEFINED_FOR_STANDARD_DEVIATION_TYPES
                     for stddev_type in stddev_types)
          std = np.zeros_like(rrup)
          std[rrup <= 20] = 0.23
          idx = (rrup > 20) & (rrup <= 30)
          std[idx] = 0.23 - 0.03 * np.log10(rrup[idx] / 20) / np.log10(30. / 20.)
          std[rrup > 30] = 0.20
          # 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 3.5.5-2 page 151