code: def _compute_term2(self, C, mag, rrup):
          
          c78_factor = (C['c7'] * np.exp(C['c8'] * mag)) ** 2
          R = np.sqrt(rrup ** 2 + c78_factor)
  
          return C['c4'] * np.log(R) + (C['c5'] + C['c6'] * mag) * rrup
docs: This computes the term f2 in equation 32, page 1021