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We present evidence that variations of ground water content play a dominant role in governing seasonal crustal deformation and changes in seismic-velocities, as measured by GNSS displacements and ambient seismic noise analyses in the tectonically active Northern Apennines of Italy. We focus on the Altotiberina fault (ATF) zone, where dense geodetic and seismic networks are part of a near fault observatory of the European Plate Observing System, and analyze 12 years of multidisciplinary data. GNSS position time series are analyzed using the Independent Component Analysis technique in order to detect the main geophysical sources that induce deformation. We identify tectonic signals associated with post-seismic deformation following the 2016 central Italy seismic sequence and with a seismic swarm that occurred in 2014 in the ATF. The largest geodetic signal is a seasonal (annual) one showing uniform …