code: def equivalent_crust_cohesion(self):
          
          deprecation("Will be moved to a function")
          if len(self.layers) > 1:
              crust = self.layer(0)
              crust_phi_r = np.radians(crust.phi)
              equivalent_cohesion = crust.cohesion + crust.k_0 * self.crust_effective_unit_weight * \
                                                      self.layer_depth(1) / 2 * np.tan(crust_phi_r)
              return equivalent_cohesion
docs: Calculate the equivalent crust cohesion strength according to Karamitros et al. 2013 sett, pg 8 eq. 14
  
          :return: equivalent cohesion [Pa]