def equivalent_crust_cohesion(self):
        """
        Calculate the equivalent crust cohesion strength according to Karamitros et al. 2013 sett, pg 8 eq. 14

        :return: equivalent cohesion [Pa]
        """
        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
Calculate the equivalent crust cohesion strength according to Karamitros et al. 2013 sett, pg 8 eq. 14

        :return: equivalent cohesion [Pa]