code: def _get_distance_term(self, C, rrup, backarc):
          
          # Geometric attenuation function
          distance_scale = -np.log10(np.sqrt(rrup ** 2 + 3600.0))
          # Anelastic attenuation in the backarc
          distance_scale[backarc] += (C["c2"] * rrup[backarc])
          # Anelastic Attenuation in the forearc
          idx = np.logical_not(backarc)
          distance_scale[idx] += (C["c1"] * rrup[idx])
          return distance_scale
docs: Returns the distance scaling term, which varies depending on whether
          the site is in the forearc or the backarc