code: def _compute_faulting_style_term(self, C, rake):
          
          if rake > -120.0 and rake <= -60.0:
              return C['aN']
          elif rake > 30.0 and rake <= 150.0:
              return C['aR']
          else:
              return C['aS']
docs: Compute faulting style term as a function of rake angle value as given
          in equation 5 page 465.