We analysed the data recorded by the NE-Italy tilt/strain gauges network in the time interval 1976-1996 (Braitenberg et al., 2006; 2019) at the light of the results of the analyses of Rossi et al. (2016; 2017; 2018) of the cGNSS at the northern tip of the Adria microplate. We considered the longest tiltmeter time series, in which long-term oscillations were previously observed (Rossi and Zadro, 1996). A transient oscillation appears to be present in the recordings of four tiltmeter sites, revealing a tilting along the tectonic features in the period 1984-1987. By using the same tomographic approach and the model of Rossi al. (2016; 2017), we located the transient’s source as originated in correspondence of the South Alpine thrust front, near its intersection with the Idrija fault, in western Slovenia, not far from the source identified by Rossi et al. (2016) for the 2006-2009 transient. The velocity field is compatibel with a fluid diffusion, confirmed by the results of the hydraulic tomographic inversion. The area, hence, would be confirmed as a source of fluid diffusion. The various thrusts and transpressive structures, involving formations with variable permeability, can act as barriers, generating overpressure conditions, and, from time to time, enable fluid diffusion in the surroundings. We calculated the fluid influx and the total discharge.
