Motion magnification technique for the monitoring of masonry structures

Motion magnification (MM) is a recently introduced technique that allows displaying small structural vibrations, otherwise imperceptible to the naked eye, by amplifying movements from videos taken with common cameras. Vibrations of structures caused by micro-earthquakes, such as traffic-induced tremors, are perceived through pixels comparison in video frames as their intensity is increased so that they become visible. Motion magnification analysis allows to identify which parts of the building are most vulnerable to earthquakes and to determine structural natural frequencies. Three simple structures are first considered to check the method reliability, then the technique is applied to different structures in situ as bell towers as well as bridges. The results show a clear correspondence between the theoretical frequencies of vibration and those identified by the processed videos. As such, motion magnification can be considered as a valid tool for a non-invasive, fast and low-cost analysis of the dynamic characteristics of buildings.