Magnetic properties have been used already for decades in detection and quantification of deformation along large geological shear zones. Now, the same analysis, including Anisotropy of Magnetic Susceptibility (AMS) and total magnetic susceptibility can be applied in geotechnical cores. The aim is seeking for changes in the orientation of particles and content of magnetic minerals in strongly deformed zones. In particular, the technique has been proven to detect micro-shear zones that might develop slope instability. The presence or horizons with a high value of the degree of anisotropy, increase of the total susceptibility and oblate (or flattened) ellipsoids of the magnetic anisotropy in cores dominated by clay and marly-clays is indicative of micro-deformations. This has been confirmed by further rock magnetic analysis showing that at those horizons also coercivity degreases and magnetic concentration increases.