code: def _get_scaling_term(self, C, rrup):
          
          a_f = 0.15 + 0.0007 * rrup
          a_f[a_f > 0.35] = 0.35
          return C["af"] + a_f
docs: Applies the Cascadia correction factor from Table 2 and the positive
          correction factor given on Page 567