Automatic modal parameter estimation is necessary for continuous structural health monitoring and damage assessment. The interpretation of stabilization diagrams is the most used tool for parametric system identification. In the present article an automated interpretation of the stability diagram is described and applied upon five years of vibration data of a building structure located in Chile which has been subjected to more than 1700 earthquakes. The automated method considers soft and hard validation criteria and three types of clustering algorithms. Results obtained from its application indicate that they are highly dependent on both the quantity and quality of the sensors, and several notes to achieve a fully functional automatic procedure are exposed.